I don't think it'd be a stretch to say that a lot of people bought Xboxes for Halo, though.
Something else to keep in mind about Sony is that Move game they're publishing featuring characters from Jak, Sly, and Ratchet. So even if they aren't tied down to one specific character, they certainly aren't ignoring their marketability. There are more than just those three of course, but it's the first example that comes to mind.