I don't deny that multi-core will become more and more prevalent, but which if Sony's games use all of the Cell's cores? Last I heard KZ2 uses 4 SPEs, and even then quite sparsely (a lot of idle time on those 4). It was on some presentation slide by Guerilla, unfortunately I can't find it right now.
EDIT - Found it:
My Mario Kart Wii friend code: 2707-1866-0957