they will ask you if this is a replacement or an add on receiver, so i don't think it makes any difference. The price seems to be based on years with E* and programming level (And CC autpay too?)...
I called today and they asked me if the 811 was going to be an add on or a replacement receiver. I told them replacement and they quoted me a $149 price with a AT50 or greater commitment for 1 year. She never mentioned anything about sending back my old receiver.
Perhaps the exchange is just for those being offered the $199 deal and they were just wondering whether or not to deactivate the old receiver off the account or not.