Lexicon & Harman/Kardon have been marketing 7.1 systems for several years before the others.. Beyond 5.1.. THX & Dolby were pushing 6.1 but it was proven early on that a center back loudspeaker often caused the rear sound field to collapse
Dolby introduced DPL2x which performs very well for post-processing 5.1 > 7.1... And now we are starting to find new HD titles with 7.1 mixes which are excellant, and even certain SD titles have been remastered
to HD with great results.
How important is 7.1 vs 5.1..
The addition of back surround L/R loudspeakers help to fill
a larger room, but a well setup 5.1 system will give it a strong run. To me the 7.1 adds some additional sonic dimensions to a 5.1 system but here again it is up to each listener.. It is crucial here not to have the back surrounds too loud which is a frequent mistake. The user should listen to both and if they can hear certain differences than go 7.1 is not stay with 5.1. Also it is getting more difficult to convince the wife about adding 1 more pair of loudspeakers.. But that is another subject in itself..
Just my $0.02 worth..