I disagree. If the course allows music to be played, isn't it up to individuals who find it distracting or distasteful to choose to play another course? I'm assuming this is not a gray area regarding the rules of the course. I think the David and Joe are right in what they're saying.
The number of people is almost irrelevant (other than common courtesy). If the rules allow it and one person wants to listen to the music, he/she has that prerogative.
I hate being around drunk people, selfish bastards, golf snobs, loud obnoxious bro's, or other's taste in music. Guess what, those people/things are at golf courses. If the course allows the type of activity or behavior I dislike, I have to suck it up or choose another activity. Others shouldn't bend to my will.
Personally, I can't imagine playing music while playing golf. But if that's the direction the golfing community and industry is headed, we'd better get used to it and hope those playing it will be considerate.
Finally, I have to believe what David is talking about and what Rick described in his original post are two different things.