Originally Posted by James
If you want the unofficial bs-corporate answer (from what I understand), it's because of copy-protection issues. Because the movie companies are insisting on a "secure channel" from the disc that is inserted, all the way through the output to the monitors and the speakers, Microsoft and hardware manufacturers have been playing it careful with everything.
So the reason they've delayed it is probably because they haven't found a way to secure the decoded output from the soundcard. (I.e. Suddenly, all of those DVD/HD rips would have beautiful surround tracks to go with them.)