When You Buy an iPod, who controls what you can play on it?

So RealNetworks, with the announcement of Harmony Technology earlier this week , makes it possible to play the music purchased from Real's music store on Apple's iPod music players.

Since this makes Apple's music player more useful to its customers, by enabling iPod owners to play music purchased from another online store on their iPods, one would think Apple wouldn't mind so much. But Apple doesn't seem too keen on Real's idea. Apple is not only threatening to make its iPods not compatible with Harmony, but also possible legal action against Real Networks as well.

Can you imagine a world where radios only played music that was also only broadcast and licensed to be distributed by the radio maker?