The audience depends on the theater and the movie. Maybe mainstream cinemas are like that. I don't understand why people pay the (apparently high) ticket prices for a movie they then don't want to appreciate. Then again, I also see a lot of people at concerts with $100 or $150 tickets who just spend two hours chatting with their friends, seemingly more upset about having to shout over the loud music than listening to a single song...
I go to the movies fairly regularly, but only small ones, which show more "artsy" movies (i.e. the only ones still worth watching anyway, IMHO) or reruns of classics. There, watching it with a room full of strangers is an upside again, or still. Because everybody there along with you is because of a shared interest, and everybody wants to be there and enjoy the film.
As for the sound systems, fair enough, but it has its limits. I find headphones uncomfortable, and they don't make sense when watching with someone. And limits on what I can do to my neighbours. One of my most recent cinema visit was for The Blues Brothers. Having that one's sound on a massive room-size system is such an important part of that movie. I couldn't have turned up the volume to a quarter of that in my apartment, because I actually like my neighbours and would like to stay there for a while longer.