Their business model seems to be working well enough for them to continue to expand their stable of shows, and to not compromise on their quality. Poor ratings don't even seem to affect them as badly now as they used to; in general, the biggest danger to an HBO show is the production costs.

As for Disney's model, it's still in operation, they've just changed the numbers. DVDs do "leave print". WB is about to do the same thing with Harry Potter. Artificial scarcity is still viable now, it's just harder.