I'd recommend calling D*, saying they replaced the HR20 with a HR22 and since they don't carry all your local ATSC HD channels on satallite yet could they please send you a AM21 for free so you get those channels back, many report getting free AM21's.
I did that today, as you said. No problem at all. Very pleasant CSR, and I didn't even go up a tier or so. What I've found with D* over the years is if you're decent to them they reciprocate.
Thanks for the advice. I know I could have done the same as the AM21 with my DTVPal units, but they wouldn't couple with the HR22-100 and the guide, nor record to the DVR. I'm good to go now.