That's why DVD won't die, or lose first spot, for a long time.
I think that when people will be able to store lots of HD movies on hard drives, maybe that's when optical formats will die.
I never understand why people keep bringing up MP3s when talking about SACD/DVDA. If anything,
MP3 ate up CD sales, not SACD/DVDA sales, which are just niche and always will be since their market is just different to the CD/MP3 market. It's like they're on a different dimension. MP3 damaged CD sales, not SACD/DVDA. What damaged SACD/DVDA is that no one gave a damn and the companies making the formats didn't convince the people that they "needed" them.
HDTV is a new standard that will become a much bigger part of our houses than "high quality audio" ever will. Even at this somewhat "initial" stage, HDTVs have made a huge impact, and eventually all TVs will be HDTVs. And people will want to play HD movies on them without much trouble and FAST, and optical formats are the easiest option.
Surely, digital distribution is the wild card, but we won't have infrastructures to support that for a while (bandwidth for fast downloads of huge files, and hard drives big enough to keep a lot of movies in there at any one time), and in the meantime HDDVD and Bluray will have a chance to make an impact.
Anyway, we've discussed this so many times...