As it turns out, HTC didn't just add a handful of its phones to its bootloader unlocking tool, it has added every phone launched since September 2011. The announcement came quietly in the sidebar on HTCDev's site, and in addition to the newer phones the company is also working to expand unlocking to more older phones as well:

All HTC Android devices launched after September 2011 are unlockable. The website will be updated accordingly to reflect this in the coming weeks. We continue to work on models launched prior to September 2011, please check back often for the status of older devices.

As the statement implies, the current listing on HTC's website doesn't include every phone that currently works, but we've seen reports that the HTC Vivid, Rezound, and Thunderbolt are all compatible. It may be a slightly convoluted process, but it's entirely a legit one and HTC deserves credit for getting it done and finding a way to ensure that carriers didn't block it.

Originally, CEO Peter Chou had promised that HTC would cease locking bootloaders entirely, but later the company hedged by offering this unlocking tool as a compromise. Whether you feel that it is a fair compromise or not, it's likely the best that HTC was able to do and still represents a fairly major philosophical difference compared to other companies. Android hackers and lovers of custom ROMs, it appears that HTC is trying very hard to get back in your good graces.