The biggest issue with making it a PS3 exclusive is the fact that the PS3 has a small user-base. But then again, exclusive games are generally MUCH BETTER than multiplatform games. Why? Because the developers need only to focus on ONE system.
For instance look at COD3. Its a decent game, but its full of bugs and multiplayer is shit. Clearly Activision doesn't give a rat's ass about the PS3 or Wii version, as evidenced by shitty multiplayer and lack of new maps or updates for the PS3 version and no multiplayer whatsoever in the Wii version.