Nick
You are probably right, in the sense that a Muso session is more or less wallpaper to a lot of people who even go to listen to the music, it is a pleasant background to the evening and, may I dare to say, quite insular. Singing is quite different, maybe for some it has to be listened to, but as I strike that drum again, singing is good for the soul and you can't beat a rousing chorus of many souls, however, I think that when it is all singing there is no room for chat and the music gives people time to chinwag which I believe is also an essential ingredient of a good night out. And, before the musos jump up and demand respect, the instruments tend to be far louder than all the noise in the bar so why not.
Peter