Maybe it's just me, but I really don't think Samus in the Zero Suit is a good example. It makes sense as something that you would be wearing under power armor like that, does it? I'm looking at an actual in-game shot from Brawl (Sorry, but the picture you used looks really fanmade to me), and it doesn't look that bad, I don't think.
I think it's a matter of context, in this case at least. I would imagine that Master Chief is wearing something skintight under his armor, too. Plus, y'know...it's Nintendo. I can't think of any other time they've designed something just to be 'sexy'.
(On another note, unless my memory is wrong, Brawl went both ways with it, and gave Snake a quite defined ass, if I'm remembering right.)
EDIT: And monobrow, can you find smaller pictures? It's making your post a bit hard to read.