I suspect the key difference might be that HTC doesn't want to release the following type of instructions: "Tap settings, Tap Applications, Tap Development, Enable USB Debugging, now install this software on your PC, connect your phone via USB, be sure to un-mount your SD card first... etc. etc." I think they would prefer to release a one shot install fix and that to my knowledge hasn't been figured out yet. In the end it may just not be worth the effort for them to do on older devices as well.
