I turn the music off on 100% of the games I play. This is true for many players. When I play games I listen to my own music in the background (my CD's that are on a playlist on my PC). So not having music in your game would save me an extra step - finding a way to turn it off.
I've always wondered about adding music - the ratio of people like me that turn it off vs the people who actually allow it to play. It would be an interesting statistic.