In my mind, the big one is that radio stations are not allowed to tell you when they're going to play certain songs. That means you'd have to put a lot of effort into recording the songs that you want. Also, radio stations are supposed to pay for songs that they broadcast, but that's mostly irrelevant because of the ``rebates'' they get from the record companies.

It's been pointed out that with today's computers and storage devices that it would be fairly trivial to record an entire day's worth of radio programming, but you'd still have to search through that entire day to find the song you were looking for and the broadcast of it has ostensibly been paid for.