Not true at all. It makes no difference what "version" of Android you are using as to whether or not you can root it. It only matters that the boot loader isn't locked and there's no tech in place (like eFuse) to brick your phone if you try and load a different ROM. HTC has been pretty good about keeping it's phones open to additional ROMs and it's not stock. I flashed Cyanogen onto my HTC Desire HD a few weeks back with no problems. I went back to the SenseUI a few days ago though because I missed the cloud integration and the stuff that people usually change Android flavors for is already in Sense or not locked out of their version of Android in Taiwan like it is in N. America or the Eurozone by telcos sometimes.

Anyway, I was referring to user experience (like integration with cloud services, GUI, etc...).