5.1 surround has become a "standard" because many home systems are 5.1, so there isn't any tweaking required when films are released on DVD. This way the studios, who HATE spending money, only have to cough up the bucks for the stereo mix.
I'll be fascinated to see if 9.1 surround ever makes it into the theatres. For those who don't know about 9.1 surround, add four more speakers left/right front and left/right rear ten or more feet above the normal left/right front and left/right rear use in 5.1. The sounds are now vertical as well as horizontal. It sounds absolutely awesome!
