Different strokes, I guess. I prefer natural-looking women too, in reality, but this isn't reality. All of it looks fake and weird. I think all the robotic-looking women in all the games you mentioned are also somewhat creepy, low-poly, and ugly. Alyx perhaps less than some, who could potentially be mildly attractive if she wasn't so fucking annoying. Seriously, the chicks in DA look totally wrong. Morrigan has lips the size of New Jersey, has ridiculous permanent eye shadow, and a nose you could slice cheese with. I don't see the appeal. Leliana (sp?) isn't so bad, but she still looks more like a mass of polygons than a woman. Same goes for all the women in Fallout 3. They only barely resemble people.
I see your point, though, W7. I don't really think that's why anime and manga chicks have big boobs, though. I'm pretty sure that's just because dudes like hooters.