Well, while a lot of characters aren't explicitly homosexual, there are also a lot of characters that aren't explicitly heterosexual.
Off the top of my head, Samus, Link, Marcus Fenix. Honestly, I don't think touting people's sexuality has any place in most games ... I'd rather they just leave it out all-together, unless a relationship is a focus of the game, in which case I don't really care which way they swing, as long as the game is good.