Do people even buy 5.1 receivers anymore? So why do studios produce DVDs with 5.1 DD or even DTS? Let's face it, only folks with any interest in the audio side of things will take advantage of surround sound, and I think most have upgraded to at least a 6.1 receiver. 6.1 discrete should now be the standard - minimum!
Let's take the Gladiator DVD for example. It came out in early 2001 I believe. That's a damn long movie, and yet they managed to cram a DTS 6.1 ES track on it that's still almost reference quality. Almost nobody owned a 6.1 system then. 5 years later, DTS ES or DD EX is still nowhere near as common as you'd expect yet everyone and their mother seems to own a receiver capable of decoding it.
What about 7.1 discrete audio? No DVDs that I know of carries it. I was quite shocked when Star Wars III came out on a stinking 5.1 mix (a damn nice sounding mix still), but being such pioneers of digital sound, I would have expected a 7.1 mix from the THX crew to serenade the release of the film. So what's the excuse? I'm baffled....