I have numerous SD receivers and a 9200 all on the same account and the HD channels only show in the guide (no matter what mode it is in) on the 9200. I can't see how the programming would be done on an individual receiver basis....it must be on an account basis.
This applies to other channels as well that you do not pay for. Some show up as "red" in the guide, but most simply don't show up at all (although I assume this is different in that the 800's some how are filtered in the non-HD firmware or some flag in the EPG info).
Movie channels (east vs west) that aren't available in your area don't show in the EPG at all.
Interactive channels may be a better analogy. They don't show up on the older (2700) models as they are not capable (or at least they weren't last time I had one on my account). Filtering of the EPG must be in the firmware based on flags.