The Ipod Shuffle is only $99 and you can store 120 songs on it.
You can change the playlist when you get bored of them.
The question is "Who listens to more than 120 songs that doesn't have the time to simply change the playlist every now and then?"
If I only wanted to listen to 120 songs, I'd listen to FM radio. That's about how big a typical FM radio playlist is.
My iPod has over 8400 songs. I like hitting Shuffle and having absolutely no idea what might come up. The best part is, any song that comes up is one that I know I'll like. It might be a current song or it might be a song from 30 years ago. I also have dozens of very eclectic playlists that I could never possibly assemble from a list of just 120 songss.
So the basic iPod shuffle is for casual music fans who don't own a lot of music. The iPod nano is adequate for most serious music enthusiasts. But the full-size iPods (like the 20gig and up models) are for music junkies like me. And there are a lot of music junkies out there.