Why do they ask for other people’s blend files? I ask as someone coming from digital illustration to 3d, confused not only here but elsewhere when people ask for working files. There’s no other visual medium where you would claim to be eager to learn, and instead of re-creating things yourself, just ask for someone else’s work to run tests over. It seems to run completely counter to the “make your own art” part.
I think it is because 3D has two components: the technical (how do you do it) and the artistic (what you do with it). People generally ask for the .blend file to learn a technique (technical). After that, it is up to the artist to make something out of it.
All art has those two components though lol. I wouldn’t go to a painter I admire and ask if I can take his painting home to trace over.
Assuming he could provide you with a perfect copy at zero effort, why not?
I kind of have to agree with you a bit on this, and it’s similar in the fractal community, they throw a lot of whole parameters around and then someone changes one number and says “look what I made!” On the complete other side of the coin, someone’s file(3D, fractal, whatever) may be quite useful, as long as someone is indeed learning from it and not actually using it in their own project. I myself really hate to see right after a guy posts a masterpiece, someone yelling “gimme blend file!”, but that’s how it goes. I’ve checked out Yafaray’s demo files, as well as other people’s files occasionally, and I learned quite a bit from them, but would never think of using any of them for anything. I can’t recall ever asking for them either. But yeah, it’s much more satisfying to experiment and learn through many trials and many errors yourself. 
That said, in traditional art, it’s a very common and long-standing tradition to “learn from the masters” by attempting to replicate the work of one of the classical master artists.
Of course, there’s a bright side and a dark side to this. On the positive end, there’s a good chance that you’ll learn to effectively wield the tools of your craft. On the negative end, there’s always the possibility that you’ll be nothing more than a skilled facsimile machine.
Really, working from someone else’s piece is nothing new and has the same potential benefits and dangers that it always has. It’s for the audience (which also consists of the art-making community) to evaluate which side of the spectrum a particular piece of work falls.
The point of taking someones .blend file is not to have some art and claim it as your own.
The point is to see how this thing is put together… For example, you have no idea how IK works on bones, but by having an example .blend you can see the setup and that’s how you learn about it…
Just to clear up, I wasn’t comparing looking at other people’s files as flat-out thievery, just meant that the files should be looked at, learned from, and interpreted from scratch on your own. But, like Fweeb said, there is a dark side to this too.
That’s exactly my point, why would I want to make art with zero effort that looks exactly like something someone else has done?! That’s weird.
While I have nothing against looking at others’ files, I don’t think it’s terribly useful except for newbies to pick up the basics. There’s a large number of factors that decide why a particular scene is constructed in a particular way, and without knowing the decision process that led to it, you don’t get the full picture.
To learn how the other guy did it and then apply that knowledge in your own art? Looking at other people’s scenes != recreating their art. If you really want a traditional art metaphor, it’d be like inspecting a painting with a magnifying glass or x-raying it.
As in many things what I see is that technology is being written off as just an extension of what’s always been done, but don’t you think it’s weird that you can’t tell most CG artists’ work apart?
Well there is always the possibility to include only the parts of particular interest in the .blend file so it’s not possible to simply make a copy of it.
Another option would be to ask the requester which part they’re interested in and post screen shots instead.
Different people are interested in doing different things. Perhaps someone likes to make beautiful scenes, but doesn’t model very well. Maybe someone is greatt making models but bad at lighting. Everybody is free to make art the way they want, right?
If you aren’t doing most of the steps you aren’t actually “making” the art. Also what you’re describing, whether you realize it or not, is someone who wants the end result without the hard work, which implies an unwillingness to learn the craft.
I think this has more to do with the fact that cg art tends to be realistic, which is probably because it is a young form of art.
That’s a good point, maybe people are more interested in imitating and re-creating than creating at this stage.
hope the OP never falls into a poser/DS forum 
most art there is from paid for or freebies
some of it very good lots not so good even though they all use the same basic building blocks
blend files are shared more to pass on the info of HOW it was made
for me its shaders lol I love em especially the “why on earth” has (s)he done that
but even with a shader I rarely use someone elses “out the box”
instead of thinking of it as cheating/sharing or robbing lol
think of it as teaching materials
3D is way more complicated than traditional media, you can’t just learn through observation alone. Try to write a python script for an IK/FK slider from scratch just by looking at a short film. How would you even know whether you need one of those in the first place? The Big Buck Bunny files have provided me with excellent guidance for things like proper mesh topology, fur material setups and rigging tricks - things you can’t pick up from just the documentation. There is intricate “machinery” behind the way a material looks or the way a character’s arm deforms and if you don’t understand how those work you’re still going to get bad results. Much like with a traced drawing, there is some semblance of quality, but most artists will be able to spot you as a phony.
There are plenty of other forms of art that are created by assembling existing assets into a new form. If you don’t know of any other visual medium where artists use other people’s work, you don’t know about very many visual media.
In any case, 3d art is not just one thing. A person might be interested in creating 3d art but not be interested in modeling. They could be very interested in animation, but not in texturing. Is a person not creating art just because they didn’t create all the assets themselves? In illustration if you want a picture of a room with furniture and some people eating a cake, you just draw the scene. In 3d work, you’re going to have to build and texture every single chair in the background, every single slice and morsel of cake, every painting on the wall, every water stain on every table, every lock of hair on every character, then assemble all of these and more into the scene, light it, render it, post-process it. In illustration that cake could be the work of a few minutes, but in 3d it could be days. If you had permission to use someone else’s chair models, or cake icing material, or carpet texture, would the final picture be less “art” than if you had made them all yourself? Or perhaps you modeled and textured everything yourself, and you have a good grasp of lighting and composition, but you’re lousy at rigging, so in order to pose the characters you used someone else’s armature. Does that invalidate any of the other work you did? Would it be tangibly better in some way if you had made that rig yourself?
As for learning from others’ files, studying another person’s .blend file can be more informative than studying, for example, someone else’s painting. Depending on the painting style, you may only be able to really see the result, not the brushstrokes and techniques that went into it. A 3d file on the other hand contains an enormous amount of accessible data. You can study the mesh topology, you can pick apart the components of a material and see how they fit together, you can see exactly where the lights are, how they work and where they point, etc. Dissecting someone else’s file can be as informative as actually watching that person work. Even if you don’t actually use the contents of the example file directly in your own work, the information you can gain from it is potentially enormous.
If you don’t want to risk people copying your artwork because you gave them the .blend file, give them a separate files designed to show only the technique they’re interested in so they can safely and easily reverse engineer it so as to do it in their own projects.
This is just how some people prefer to learn (and indeed for complex files it might be needed so you can figure out what each component does and why it is there).
If you look at Blendswap, some people make it their hobby to create assets that others can download the .blend for, there are some who are simply more into the idea of sharing their work in this manner than others.