Well this is what you said in your post....
"Two years ago they did a free swap for my HR10-250 and gave me a free HR21-100. I moved my old HR10-250 to the basement."
So you didn't really swap you just received an additional free HR21-100 and moved the HR10-250 to your basement, right? Now you are calling back in and saying I have this old HR10-250, what can I get for it? So are you even swapping the HR10-250 now or will you really now have 3 receivers, HR 10, HR 21, and HR 20?
Maybe we're misunderstanding what you really did in your first 'swap'.
You're putting words into his mouth - He called and asked what deal was available. I don't see anywhere in his initial post that he asked for a second swap out of the HR10..he simply asked what deals he qualified for. If DTV did their job right in the first place, his HR10 would have been flagged on his account as having been "swapped" and since he received a replacement HD DVR, it's likely a Loyal Customer offer, not a HR10 "swap". If DTV didn't do their job correctly on the initial swap, then they have no one to blame but themselves if they offer up another new "swap" when they shouldn't have.
Motto of the story, don't be afraid to ask what DTV is willing to offer. Things change all the time. They always have the right to say no as well.