Just to add to the confusion:
“On Standard-Def DVD, there are essentially only two competing sound formats to choose from: Dolby Digital or DTS.[...]The reality of the situation is that both Dolby Digital and DTS are capable of delivering very good, sometimes even exceptional sound quality on DVD.[...]The advent of Blu-ray and HD DVD has brought a dramatic increase in picture quality from Standard Definition to High Definition.[...]High Definition video deserves High Definition audio to go with it.”
And thus begins the litany of the seven different options for audio tracks on HD discs, and how they’re supported on HD DVD vs. Blu-ray.