Hi Lisa,
Music can be used as a form of background support while studying. I control the selection and volume of music when my students are in the study mode. I don't allow ear buds or ipods in class. I want them, just as you do to be engaged in the class. Also, with their personal selection of music they may not be able to focus on the course content due to the beat or volume of the music. The students may not ever listen to the music I select on their own but that is ok because I am setting the tone for the class so I select music that calms and helps them focus. When they are on their own time they can crank it up and go for whatever type of music they want.
Gary