I bet all these games could have been multiplateform PS360+Wii
I doubt it (not that they couldn't have been ported but that a bit of Nintendo pushing would suffice)
Developing a PS360 game means you have to rewrite the engine (unless you use middleware like Unreal-Engine) but you can reuse the same artwork and the game will be more or less identical.
If you want to port it to the Wii you have to redo everything and compared to the PS360 it will look bad. So I think many developers make the decision: If they have to redo the work anyway why not create a completely unique game for the Wii that caters to its strengths (motion controls) instead of simply sacrificing the strength of the PS360 (raw power for awesome graphics, physics etc.)
I really doubt that getting ports of GTA4 or Call of Duty4 would have helped the Wii. The games would look terrible in comparison and the gameplay is suited for standard controlers anyway so the Wii advantage would fall flat. But we will see how the Wii will fare with multiplatforms like Force Unleashed and Call of Duty5. I am pretty sure the PS360 versions will kill the Wii version of both.