It seems that HTC has learned their lesson from the latest uproar about the G2 having rooting blocked, while the source code wasn't public. Now they are making public the source code for their latest 2 phones G2 and Desire Z, and also the older Incredible.
I think the reason why HTC is actually proactive about this now is that they've realized that the more open their phone is, the more it will get adopted by the developer community. This will create all sorts of custom ROM's for their phones. This ends up pleasing consumers, who will buy even more HTC phones. If only other manufacturers were as smart about this as they are, especially those companies who don't bother to give updates very quickly. At least this way, the consumer will be happy with getting an update through a custom ROM.