It's the nature of the art, isn't it? Video games often have comic book-like concept art, and in general, the finished 3d characters follow many of the conventions of such art, namely, exaggeration. Comic art is the simplification of a lot of complex detailing, so that you end up with large noses, mustaches, hair, breasts, shoulders, arms, etc just so your reader has some way to differentiate a lot of characters that lack many of the defining characteristics that makes you look so different from your neighbor.
If your every day concept artist drew someone who actually looked like a real woman instead of what they saw in a porno mag, then it'd probably get made that way. Unless the character model artists screwed with it. What I wonder is whether the presence of so many stacked female video game characters is an indicator of lack of women holding concept and 3d artist jobs, or if it's simply that everyone is drawing to this preconceived standard, even the women.
