Eh, we don't even need to go into game soundtracks to talk about explicit lyrics or anything. Just look at the last five years of mainstream pop culture music, all the rap and hiphop and r&b with lyrics talking bluntly about sex, sodomy, BDSM, murder, and whatnot. And you can't avoid hearing that stuff anywhere you go that has 'lounge' music.
Okay, so maybe a game like Sonic shouldn't have lyrics like that, but eh, not too many kids listen to the games at all. It's the adult audience that pays more attention to such details.