I'm not interested in HD/XM/etc because right now, I'm getting excellent fidelity and a variety of feeds directly from the internet. Most notably, a number of the university FM stations are now on the 'net with excellently-engineered streams.
I find that a number of the feeds, though, have not figured out how to engineer the audio for digital transmission.
Main reasons why most folks haven't figured this out:
* Its still tricky to get it up and running. Cutting/pasting URLs, dinking around with codecs, etc will keep your joe-consumer away
* Its not well known: Many folks I talk to - and I'm from the high tech world - don't know about this or don't have their home theater connected to their computer - see item above for reason.
* HD/XM/etc have far better marketing: Face it, you have to be a geek to want this sort of thing.
Cheers,
David