I've been reading about this on Penny Arcade today and really, really agree with them...
After you get past Kratos and "that guy from God of War", you don't really have a whole lot of Playstation exclusive characters that are horribly memorable... I mean look, they had to rip Parappa out of his long slumber just to help fill out the roster. And I know I saw a Helghast from Killzone pictured behind the guy near the end of the video, so there's that. I figure Ratchet &/or Clank will make an appearance somehow at least as well.
But after that, who's left? When you think of heavyweight Nintendo characters, you can't really ever fall short of 10 at minimum just off the top of your head, but not really with Sony...