Let's put it this way, if you get an XBOX360 now, you'll enjoy it.
When you get a PS3 later, you'll most likely stop playing your 360, because the PS3 will be better,
later.
It's not about how many exclusives -will- be on the PS3, but about how many games you'll enjoy on it.
Exclusive means that that game will only be on one system. So God of War 2 is exclusive to the PS2 because you can only play it on the PS2 AND the PS3. A multiplatform game is exactly what it sounds like, the game is on multiple systems.
Fixed.
All previous games on the PS2 you can play on the PS3 as well.
So you already can choose from a large library of games from the PS2 if you like any games that were released on the PS2.
Same for the 360 as well, I heard some 360 official didn't think that backwards compatibility was important anymore. (Playing games from a previous system)
Not too sure if that is true though, who said it.