Tom Watson blogs today about Howard Stern's announcement that he's leaving "free" radio for satellite. He compares the growth of satellite to cable, and mentions the cost/necessity of having multiple fees and receivers (as opposed to having many, relatively cheap radios that you can take anywhere).
I think the real story is the growth of the fragmentation of society. Way back when, you had a melange of musical genres and tastes on each station. Yes, some played "Free Bird" and "Stairway to Heaven" until you wanted to kill, but a quick flick down (or up) the dial brought you another song. Exposure was the serendipitous result - finding something or someone new to listen to and learn about. That's a lot harder to find today.
Why is this a problem? While the majority of us still use the radio, the homogenization of music means that the "aha" moment is removed. Those that opt for XM or Sirius remove that almost entirely, as they narrowly program their tastes and excise what they don't know.
One of my professors in graduate school thought this was an exciting development, that soon we could drive across country and only hear the music we wanted. That thought scares me. Diversity breeds knowledge and potential acceptance of the "other." Narrowing our choices (on the radio, tv, in life) ultimately hurts everyone.