That's not true at all. You need a custom recovery, like Clockwork Mod Recovery (same dev as ROM Manager, but not the same thing), Team Win Recovery Project, or 4EXT (etc.), but you don't need to have ROM Manager installed at all to use any of these (they can be flashed from the terminal or ADB). Also, you can revert to stock by placing an update.zip on the root of the SD card and booting into HBOOT on most phones, or by using Odin on Samsung phones as previously mentioned.

Actually, it doesn't even include all of their Android phones either, take a look at the link. The Amaze 4G, EVO 3D, EVO 4G, EVO Design, EVO View 4G, Flyer, MyTouch Slide 4G, S710d, and Sensation are the only phones listed. Also worth noting is that you have to register a developer's account and send your device ID to HTC to get the proper unlock file back. While allowing users to unlock their phones is great, I'll stick to the traditional method of using third party tools.

Well, you could at least play a decent MMO if you're going to...