I'm not sure I buy that. The upgrade from CD to SACD is marginal at best, and requires special, expensive equipment. The upgrade from CD to DVD-Audio is significant, but requires significantly more labor to make worthwhile. (I'm thinking specifically of having more than two channels, not the different sample rates.) Part of the lack of acceptance for both of them is the scant number of releases for either of them. The upgrade to an iPod is about convenience rather than quality. Basically, I don't see the iPod and SACD/DVD-Audio as being competing technologies.

On the other hand, the upgrade from DVD to hi-def DVD (whichever) is significant to all but the blindest of us, I think. In addition, most people will upgrade to some sort of HD solution in the future, mostly as a force of the marketplace as a result of the manufacturers' compliance with FCC regs. I imagine that, before too long, all TVs sold will be HD and all DVD players will play hi-def DVDs and lo-def DVDs because it will be cheaper for the manufacturers to make one product than two. As such, you will reasonably quickly have a large set of people who have the appropriate equipment, as opposed to the acceptance of SACD players, which has no popular push behind it. In addition, while it may take more processing time to master a hi-def DVD, it doesn't take any more labor, so I doubt that there will be a dearth of hi-def DVDs available for rent and sale. What would definitely make it take off is if they were also readable by lo-def DVD players so that there would be no need for manufacturers to make two different media, but, then again, they produce movies as UMDs in reasonably high numbers, which is going to be a niche market in perpetuity, so I doubt there's a concern there. And there are lots of people now who buy DVDs and have a TiVo, so I don't see that having both is an impediment in any way.

The problem I see is if the marketplace starts selling lots of TVs that downconvert everything to 540p or something in order to save on the price of hi-def displays. Another problem would be the availability of broad on-demand capability.