Thanks for the update. Isn't the Eastern Arc all MPEG4 now? Are there more subs that use the Western Arc? Living on the West Coast (Oregon), I can use either Arc's but the Westerb Arc is higher so less apt to get rainfade.
Once they formally started putting people on eastern arc years ago, yes, they made it a requirement to get the newer equipment for MPEG4... so while there could be a few legacy mixed arc/custom install scenarios... officially anyone on eastern arc is required to have the newer equipment.
Western arc, though, still has a lot of subscribers... and even people with a primary MPEG4 receiver on western arc might still have some legacy equipment in use too for other rooms.
Dish tries to entice people to swap to things like the Hopper partially to get that system out there but also to upgrade those folk... There will one day be a tipping point where less people are left to upgrade OR costs of satellite launch are prohibitive by comparison OR they are willing to cut and run on customers who don't want to upgrade... but we are likely years away from that point.
IF Dish takes the hard-line too soon to "force" people to swap out equipment... those customers might decide to switch to cable, DirecTV, or cut the cord altogether... so Dish has to be careful applying too much pressure too soon.