Hmm - that is probably why Dish is only giving out leased receivers as replacements.
You have these old, obsolete satellite receivers that people own - they have gotten years of use out of them, and they may be close to failing.
Dish is perfectly willing to replace that old receiver with the latest model equivalent receiver - but they only want to do that for people who are using the receivers to get programming.
If they replace with the latest model receiver on an "owned" basis, then there is nothing preventing people from immediately selling them on ebay, rather than using them to get programming.
The more I think about it, the more likely it seems that is the reason. Dish would lose several hundred dollars of manufacturing cost - for no return.
PS I received a 522 for my 721. It is exactly the same front as the 721, except black, and I am already using the second output. The same remote and same Onscreen interface as the 622 makes it easier for the family (no more having to press "stop" to get out of playback).
My monthly bill is exactly the same - the $5 "additional receiver fee" now has a different name.