The difference is that with piracy, there is a chance you'll stumble upon something new. With the radio, you're stuck with the same handful of songs over and over and over again.

But seriously, I have always wondered how the radio model is supposed to work. Whenever I hear a song I like, just wait an hour, and I'll hear it again. There is simply no reason to buy the CD (or record, or digital download).

Value is, in part, driven by scarcity. When you only have 40 songs in your rotation, there is no longer that scarcity required to drive the high value. It's no wonder people were no longer willing to pay $20 for a CD.