The other thing to consider is the 100% certainty that purchasers of the 360 HD-DVD add-on are buying the drive to watch HD-DVD movies. There is no such hard data concerning Blu-ray movie use for PS3 purchasers.
The software for the PS3 will eventually come up to speed. However, my original point remains valid - all of the gaming software in the world doesn't mean squat if you can't buy the console due to lack of availability.
You're paying as much for the XBox 360 + HD-DVD add-on as you are for a PS3. The XBox has absolutely zero price advantage as a high-def disc player if you're wading into the pool for the first time.