Actually, in response to MusedMoose and Suzaku, fixing model artwork in Warcraft is not an artistic challenge at all. It is solely a programming one. You see, everything in WoW, from the base models to the gear, is key-framed. That means for each and every unique character model and each and every animation, each piece of unique mesh needs to have it's position for each frame recorded. Granted, this process can be easily automated, but it's a throwback to the 1990's before we had Vertex Shaders, screens bigger than 1024x768, and processers pushing the 800MHz mark. Essentially, the majority of WoW's rendering hasn't changed since Warcraft 3 in terms of the algorithms involved. Applications like the WoW Model Viewer are a great resource for seeing these individual combinations of states and frames.

Changing the models themselves would be easy. Updating the graphics engine from a keyframed one to a physics-alike procedural shader based one is a massive challenge- and it would be a destructive one.

And it's a challenge that Blizzard has job postings to try and fix. (Yes, I applied, but I think I was a bit too new in the business to qualify. They want people with previous game development. Fun Fact for Trivial Pursuit: to get into the game design industry, you must first have experience in the game design industry!)