Well, this is a bit OT, but here goes.
I think people still buy CD's, in fact sales figures are higher than anticipated (in the post-mp3 realm). DVD's are hot because of several things - one of which is the transition from godawful VHS quality. DVD's are more compact, more attractively packaged (and marketed), feature tons of bonus garbage that compels people to buy (even if most people aren't fans of trailers, unfunny bloopers, rightly deleted scenes, and over-zealous commentary tracks). During the laserdisc revolution, this treatment was reserved for films which really have something special going on, but I suspect even "Chainsaw Hooker Trash From Mars, Part III: The Manifest" (or whatever) will stroke itself with just any junk lying around the studio that might be considered "collectors rarities". See how many of these extras you can stomach consecutively. Even on my fav films, most of that stuff belongs in the trash bins. I am, however, a seriously hardcore trailer collector. Go figure...
I don't see the DVD revolution as having anything to do with any of this, though.