I've said this countless times already but I guess I can again:
Porn is a help, sure. But porn today != porn of the early 80s when VHS/Betamax were going at it. Before then, getting porn into the household had pretty much no other avenue. Today, we've got VHS, DVD and the internet, and HD porn is readily available on the internet.
Besides that, DVD is just as good for porn...most people watching a porn aren't watching it for the detail and for how good the audio sounds.
HD DVD isn't going to be saved by porn, but it certainly will help. Price of players and availability of (non-porn) titles is far more important.