Oops, i’ve been mis-gendering Helge – sorry! 
The rules post is dated May 2002, so this was started roughly the same time as the Blender Foundation, wow! Is it about time for an update? There’s a bunch of stuff about image posting that doesn’t apply anymore, for example. The bit on making new stuff is expressed as “new models”, which made sense over ten years before Grease Pencil was artistically viable. But now it comes across as kinda exclusionary (IMHO), and Blender’s texture/material making have advanced enough that it’s a reasonable purity expectation.
That’s aside from things like “foreground” and “background” being used confusingly outside of their usual meaning ( “I like to read ‘foreground models’ as ‘important parts of the entry’.” – great, I’d like to see it described as “important parts of the entry” in the rules post). With an artist’s back catalogue mostly off-limits, the Weekend Challenge is uniquely newbie-friendly – it seems a shame that the rules-post isn’t anymore. I know it’s just a fun little challenge and nobody wants to get into strict rule-mongering, but given how often questions have been coming up maybe improved clarity would be helpful.