If the communication between the Hopper3 and the Joey3 did not change from the Joey2 then why did Dish have to update the software in the Hopper3 for the Joey3?
My assumption would be that the update was to enable the Hopper 3 to even be able to look for Joey 3s on the moca network, even if the method of communication did not change.
HEVC is almost certainly for forwards compatibility. The more HEVC boxes Dish can get out there now, the less pain there is on the backend for when they actually make the change. Imagine how much more quickly Dish could convert the western arc away from MPEG2 had they gotten MPEG4 boxes out there two years earlier.