I think this has been one of the major innovations of the iPhone: not allowing carriers to tamper with it.
MS understood this and they are doing the same with WP7. Google knows it is a problem so they release the Google Experience phones, but they can’t disallow it completely.
I think it's quite interesting to see google go the same route as MS did with Windows and Windows Mobile which is allow the OEM to customize to make money, while letting user satisfaction drop. At the same time, WP7 is a total different strategy to tightly control the hardware and give a much greater user experience while the OEMs have less and less control.
MS understood this and they are doing the same with WP7. Google knows it is a problem so they release the Google Experience phones, but they can’t disallow it completely.