It looks like they're going for a more realistic look with the new art. The eyes and nose are noticeably toned down from the slight 'anime' look of the old art.
How come the official site still has the old art? I just checked again.... I check everyday to see if they added some new stuff.... And that small picture, it could just be a filter... Knowing Square Enix, they would never redesign, just make new art instead of altering old.... I'd say it's just because of the yellow filter.... Look at Vaan:
Couldn't agree more. The newer version of the first pic is much better, with the second new pic looking much worse (though that specific pic never looked good in the first place :b)