i wear headphones. i ride in the city. i like it. i used to ride with a crappy cd player with no skip protection back in the day, and before that, a walkman thing. i've always done it, and feel it too quiet when i'm not listening to something.
it's a personal choice, very much like my ride or my decision to wear a helmet and ride with brakes. everyone says it doesn't matter what you do, as long as you're riding. i agree.