Probably the same reason DTS-HD MA and PCM is hard to find on HD DVD
Looks to me like audio technologies are choosing sides in the format war too
...or maybe its just a coincidence.
Anyway, its one of the factors that drew me away from HD DVD
and has me purchasing more Blu-Ray titles now.
I prefer DTS over Dolby
My PS3 will De-Code and play all audio tracks, and has HDMI
XBOX 360+HD DVD only plays DD5.1 through digi/opt
....no matter what audio source is chosen on an HD DVD.
I'm stock piling all the DTS-HD MA and PCM titles
while patiently waiting for a new 1.3 HDMI / 1080p 7.1 Yamaha AVR