I guess it depends on the final use: close up shots for composition in a real environment requires far more detail (depending on the shot and viewpoint) than a vehicle used in the background of a shot. For a realistic looking war game you would have to model most details, and create a normal map that is applied to a lower poly model.
Really, it depends on the purpose and use. If you are going for realism (as you mentioned in your first post), you would have to at least create a realistic looking detailed exterior, of course. Interior would be unnecessary, and a waste of your time. The model in the thread you looked at is obviously meant as a goal in itself.
For example, I am working on a age of sail ship that includes almost all the details - because I want it to be completely historically correct. But this would be a useless and extravagant endeavour that takes up way too much time for a single render of the exterior!
So I believe one should model all the details one needs - and no more. And if that means modeling everything from the perspective of a historically “perfect” model: that’s quite alright. And if you just need the exterior to look right viewed on one side for an animation: that’s great as well.
ps I like this one:
Even the weld points are modeled.