I think it would be wise for Dish to move towards the 622 as their sole set top box.
1. It actually works pretty good. (reduced support costs)
2. It has MPEG4 (saves Bandwidth, increases capability of existing satellites)
3. It has HD (they can get the HD $$$)
4. It is a DVR (they get the DVR Fee)
5. It has VoD (Potential revenue source)
6. It has an Ethernet Jack (numerous potential broadband uses)
7. It supports two TVs (reduced deployment costs)
8. It has a USB 2.0 port (Ext Storage, Pocket Dish, and future uses)
Basically if they make this their base receiver, it will have all the features that could want to bring in revenue, and they'd save the money on not having to support numerous receivers. If they phase out all of the SD only receivers and replace them with 622, the can move all the SD channels to MPEG4, and kill off having to support all of those past SD only models.
Plus they can get revenue from the features that the 622 brings into the home, such as HD, DVR fee, and VoD. Not to mention whatever they end up doing with the ethernet and usb ports.
In Short: I expect these "upgrade to a 622" receiver offers to be around for while, just because it makes sense for them in the long run.