"Don't you think that the combined profit to be made from making a game PS3/360 multiplatform is a stronger adversary in itself for the Wii than the PSP was for the NDS?"
Good question. At least in US I believe most gamers will end up with a wii and a PS3 or 360. I think it's safe to predict that a game like CoD5 will easily sell more on 360/ps3 combine than wii alone.