I have been using 5.1 for decades. I didn't feel the need to add the extra channels, and most high-rez or multichannel music is only in 5.1 anyway. I mainly listen to classical music and there are a lott of lossless, high-rez recordings available. I can tell the difference, but I have always had good hearing.
However, I know few people who listen to their movies in surround sound. Most of them don't even bother to calibrate their TVs and leave them on "torch mode". Just because a lot of people are satisfied with a 79ยข speaker does not mean everybody else should be.
I have also been using 5.1 for a long time. There is a very marginal change going to 7.2 or 9.2 or 11.2 or 13.2 and IMHO not worth the extra wiring/speakers/loss of WAF/etc. (WAF = Wife Acceptance Factor) Makes me think of razors. Now with 23 blades for an even closer shave. (after the 3rd blade more blades are teats on a boar) Next week someone brings out a 24 blade razor and it keeps going.