Hi Dan,
Actually, I've been stating for years in Axiom newsletters and here on the forums that the vast majority of movies are mixed in Dolby 5.1.
The latter has been the Dolby soundtrack HD standard for broadcast, cable, and cinemas for years. It's a matter of studio mixing costs for marginal returns. The extra channels of 7.1 in home installations have been interpolated from the main surround channels of 5.1. The additional rear speakers in a 7.1 installation can certainly improve coverage in larger rooms.
Given the costs for studio mixing, I doubt we're going to see many discrete 7.1 mixes except for video games.
Regards,
Alan
