Hardware revisions are usually done because of the advancements in the production process. It's now cooloer, needs less power and it's cheaper to manufacture. I don't think the 360 had that many hardware revisions compared to a Sony or other console.
Nintendo DS, DSLite, DSi , DSiXL and the upcoming 3DS. It's all DS, but with various hardware modifications.
The PlayStation 2 has been under revision about 18 times in its life span.
i would buy a new wii if they made some major changes to the current console without coming out with an entirely new system. well only if i could softmod it!!!!
I wouldn't want to buy a new revision of any console or handheld at all. I hate paying twice for the same and maybe a very very tiny feature (camera, kinect connector, usb port, stuff like that) extra.