Well, as far as people upgrading to HD-DVD/Blu-Ray from their DVDs, I think people are going to be much slower in adopting to a new format than they were to DVD for a number of reasons that have already been covered ad nauseum. Not enough people with HDTVs, it's too soon, etc. But one of these is definitely what MAF brings up: Price. Which also ties in with the cheap and free DVDs.
Up until about five years ago, I had no problem spending $25 and up on DVD. Of course I'd always shop for the cheapest price, but $25 was pretty average for a DVD. $35 and up if you bought a Criterion. Now however, I hardly ever spend over $15 and almost never above $20 for one. The new formats are really going to struggle until people can pick them up at Target for the $10-$15 bucks they've become accustomed to.