At the end of the day - it's the publishers and investors who get to say which console a developer should build the game on.
Why depend on large install base? Because if you have a niche game like Virtua Fighter 5, your best bet is to put it in the console with the largest install base - either PS2 or 360.
However, since PS2 is soon to be in its dying throes - it's a smarter move to build the game for a next gen console that will have more legs than the currently 7 year old PS2.
Sega chose PS3 as the console to build for - no wonder they later wanted to port it to 360.
Forget what a developer said - remember what Mikami said about not porting RE4 to PS2? Yeah - Capcom sure didn't buy that. PS2 version outsold Gamecube version in a few months and thanks to PS2 version, RE4 was sold for more than 3 mil copies worldwide.
So yeah, forget what developers said abut exclusivity - it's bullcrap unless they're first party developers.
Essay Pro