DVD took off once Disney and Dreamworks stopped sucking on the DIVX teet (DIVX disc format that was released when DVDs were, and NOT the DiVx codec you use now), and started to release their titles on standard DVD, THEY (Disney) are the difference makers, not pornographers. And as dgrycan pointed out, Star Wars, the Bond Movies, the Toy Stories (ALL PIXAR), and the like are the difference makers.
Porn is more readily, and less conspicuously, available for download online. That is why they won't have anything close to the effect the had on the Beta/VHS issue. Sony made the mistake back then with the BetaMax and didn't have the studio support they have now with Blu-ray. Couple that with JVC licensing out the VHS technology, it spelled "doom" for BetaMax. That is not the case this time. (While there are a bunch of articles that suggest otherwise, here is someone who agrees that porn will not be the decider. http://www.wired.com/culture/lifesty.../2007/02/72625 )
Could HD-DVD turn it around? Sure it's possible, but not likely. Both formats have been out nearly a year and Blu-ray software is selling better than HD-DVD, and it doesn't look as though that is going to change anytime soon.
Heck, even Uni, the LONE HD-DVD ONLY MAJOR, is feeling the costly sting of the format. They announced a great deal of catalog and new titles coming out this year, and quite a few of them are NOT SD-DVD/HD-DVD COMBO discs they've been priding themselves on. They did this because the combo discs are sometimes as much as $10 more than their HD-DVD only counterparts. (I should also note that Uni isn't the only studio releasing these combo discs, as Warners is as well. But WB is format neutral, so they burden is more on Uni.)