Obviously, certain color palates can bring about different experiences for theatrical or emotional effect. In the two Diablo III screen shots above , I really do prefer the darker and grittier atmosphere (although, shockingly enough, I get a '90s game vibe out of it. I tend to gravitate towards it). But if viewed as a whole game, such as how that level is making me feel in contrast to the levels that come before and after, the color choice might be completely appropriate for what the designers intend.
Now, of course I can't say that for sure, but I can't judge a single screenshot on color choices if I can’t perceive the whole. If their intent is to use the established WoW style and hopefully attract WoW players, then I would say that they are paying too much attention to market rather than game design.
Same goes for the V13 concepts. Hypothetically in the game, we as players may have been seeing our expected and well loved wasteland visuals and encountered this strange area. But, I'll stop, going on about what is unknown is kind of pointless, as long as everyone is willing to see both sides of the coin, I’m happy.
I kind of like the plants and the idea of "rebuilding" and "growth." After so many years, society would probably continue to rebuild its self in a much larger way than BOS, NCR, or Vault City. I think there's possibility for some interesting narrative there. Hell, that'll probably be the explanation as to why there are so many people in the wasteland.