I'm one of the few apparently that do not get swayed by cost. Being able to record 4 shows at once with the 722K will keep me at Dish, as well as more non-sports HD.
For the $6 extra to have a 2nd receiver is worth it. That way you get 4 HD satellite recordings, and not limited to the OTA for 2 of them. Though it comes down to personal preference. They are not that dis-similar overall. So if the cost isn't swaying someone, the functionality is what would likely determine the outcome.