Part of the Holy Trinity
I'm sure the resounding response to this will be "about bloody time!"
Since Android came along I know a lot of technically literate people who deal with their phones on three levels. The phone manufacturer provides hardware and nothing else, the phone company provides the comms and nothing else, and then they bed down with a modding group or two for the OS. If you can do it, it's ideal as then you have fealty to no one supplier and can pick and choose parts of that package as it suits you.
If HTC follow through with this (fully) then they're certainly top of my list as the hardware supplier from now on.