I think another thing that helps is that the house is already wired for satellite in most of the rooms where it would make sense. But if the dish is already up, does that mean that all they would need is the receivers and a call to D* to activate service?
If you sell to a D* subscriber, he can connect his already-active equipment on move-in day, and call to change the address on the account. If the buyer isn't a subscriber but wants D*, then he won't need to replace the dish.... although a free replacement and installation would be part of his newcomer package.