I bought my PS3 for Folklore, Final Fantasy, Valkyria Chronicles, the eventual (and ever less likely not really promising) promise of Kingdom Hearts.
Out of my control that FF went multi and was less then astounding.
I'd say Folklore alone was reason enough for me to not get an xBox instead though.
Don't really care about infamous, tried the first, can't get over how much I dislike it to push on through it to try the second.
Resistance looked pretty decent but I don't shoot on consoles, only mouse and keyboard for me.
Killzone just looked like more shooting, would only touch it on PC.
Uncharted just came across as Prince of persia minus everything I liked about the game plus guns that I don't like, characters that I don't like, and on a controller.
The other reason is all of my friends have a PS3.
I'm a PC gamer though so the PS3 and xBox are purely exclusive boxes, I like the few on the PS3 more than the xBox because Mass Effect is a PC game and didn't count as an exclusive.