Have iPods really changed the world, or have they just sold well?
When I had a discman and I wanted to listen to music, guess what I had to choose from? One burned CD if I was lucky, and Mutter by Rammstein if I was slightly less lucky. When I have an iPod or iPhone and I want to listen to music, I can choose any song I own.
I suppose the majority of people are commuters, so maybe commuting alone is sufficient to explains the high market penetration of iPods.