The software industry realized it ages ago, and made upgrade licenses available on the cheap, out of respect for the customers who forked over their hard-earned cash. It ensured that the new work got paid for, but the customer didn't feel screwed at the same time. Hollywood isn't so altruistic, and I think it's really going to bite them hard. They're going to need to do MUCH MUCH MUCH more than just higher video resolution to make HD & Blu Ray worth it to the customers. The content is going to have to be light years better than what's provided on DVD, and with some titles (Lord of the Rings for example) that'll be an insanely tall order to fill.
I go back to the issue of seamless branching. Star Wars, Lord of the Rings, Harry Potter ... these will need to have original/special edition content all on the same disc with tons of audio options. And the extras will need to be massive archival releases never before imagined. Everything that has been collected and passed around here would need to make it onto the Star Wars HD set to keep fans from being pissed about being asked to buy yet another retread with some new continuity-destroyer added in.
I don't suspect we'll ever see an official DVD release of the O-OT, but I actually am expecting it on HD format. And pursuant to what I said above, THAT would make me want to go out and plunk down my money again. Do it with seamless branching so the different versions are on one disc and I'll really be there singing its praises ... just so long as they don't have technical screw ups like they did on the 2004 DVD.