I didn't read all of it, but I'm agreeing with you anyway...
If all of the games were multiplatform, then everyone would use common sense, and go for the cheapest console, since it can play all the other games same as the other ones, which is pointless.
Exclusive games are what seperate the consoles, and help to justify a purchase, for example, I bought a PS3 because I love the games that are exclusive to Sony, and knew they'd be making their way onto the PS3, whereas if I'd bought a 360/Wii I'd never be able to play them.
PS. I have a 360 and Wii too, was just using that as an example.