Quote - - A work where you spend two weeks doing it is better than another one done in only five minutes???

generally?  yes. 

Quote - - The joint bends bad, the hair doesn't look good, so you spend many hours in Photoshop correcting this. Meantime you forgot that the whole figure doesn't match the background image used.

um, not  so much.  if my background doesn't match, that's an error, but i've never once not worked on avoiding that.  not to mention, i've never once seen joints and hair that couldn't use work unless it was a very morphed figure or a custom made (as in modeled in that pose) figure.  actually, i've only seen perfect CG hair a few times.  and never once here.  since i'm not a huge fan of about 99% of purely rendered hair on CG society, i'd have to say i don't think it's a matter of working harder in 3d.

Quote - - You use post=work to correct some error, but in a purist sense the error still exist and the correction process introduce new errors. The question is, the sum of these new errors is better than the original error?
The only way to not create more errors is to not do the original error or at least make it not visible!

nice idea, but i've pretty much never seen it done.  in a purist sense the error still exists?  not, really.  i mean, the quality of corrections is debateable, but it doesn't "still exist" just because of where you corrected it. 

and frankly, this happens more in 3d than in 2d postwork.  V4 is a "correction" of V3, but i could name as many errors in V4 as in V3, and in precisely the areas they sought to correct.  her shoulders for instance.

and most of the time, yeah, imho, the sum of the errors made in 3d and those made in post errors is much better.

Quote - - Errors are part of our life, world is not perfect and is full of imperfections. A perfect 3d sceme looks artificial.

by definition, that's only true if you meant it to be artificial looking. otherwise, the errors are in fact the parts that look artificial. 

Quote - - Why do you look at a Greek statue? It has no arms and in most cases has no head, so it needs some post-worked head!

lots of greek statues are still perfectly in tact.  and most i've seen have much more accurate anatomy than more than half of the 3d models  i've seen, and all of the Poser models i know of.  not to mention what you can learn about dynamic posing and timeless aesthetics.    when a work has been created hundreds or even thousands of years ago and it still amazes and and impresses people, it's probably a good idea to study it and figure out what it does that has kept it so consistently popular.