I found the Xbox360 UI to be atrocious, actually. Why does the green X button turn the system on and off? Why are there 6 different versions of the Marketplace,

I found the Xbox360 UI to be atrocious, actually. Why does the green X button turn the system on and off? Why are there 6 different versions of the Marketplace, none of them consistent? Why are there ads everywhere? I enjoy the games themselves but the design seems extremely ad-hoc.