This wouldn't be surprising to me as a GSM phone is easier to release than trying to figure out how to mate the CDMA technology to the phone. By releasing it on TMo, the phone can come out sooner than it would on VZW. Makes sense to me. Besides, TMo helped put HTC on the map with Android. I see it as a class-act loyalty move! Good for you HTC!
This would also be a reason why the HTC VZW phone is delayed until April.