I don't think they are obligated to support any product indefinitely, regardless of the underlying causes. Technology marches on.
Think of HD DVD. Willfully dropped. No more s/w, soon no more updates, soon no more online features support. Slow reduction of capabilities. That's life. Youse pays youse money, youse takes youse chances.
MPEG-2 only Tivos are becoming worth less every day, at least the ones for D*. Do you think Tivo is going to hand out new ones in exchange for the old?
As MPEG-4 spreads, lots of old machines will become useless. They aren't making any offers because they have to. They're making them for customer satisfaction, which they hope will translate into customer retention. And yes, they are "willfully" making that change.
Sure, you can keep it as your property, for whatever value you see in it. And you can cancel at any time. You just might need to pay a cancellation fee.
The 5xx series is not long for this world either. Even without MPEG-4 concerns, do they have the memory and processing power to support future encryption methods? For that matter, does anyone know if any 5xx units have rec'd the new purple cards?
Didn't someone once figure there weren't much more than 100,000 721s still active? I suspect Dish was planning to phase them out, just to cut the support costs. Haven't we been hearing hints and rumors on this for the last year or two, at least? All the pre-ViP series receivers are on the chopping block. It's just a matter of when. Anyone think there's much over 5 years to go before MPEG-4 spreads so much as to drive the old receivers out of service?