They lightly touch on services like Last.fm and Spotify here, but I really think that's where the industry is headed. Yes, people are opting in for 'all-encompassing' devices like smartphones to play their mp3s, but I think even the idea of playing mp3s stored on a device is dying out. Streaming music is where everything is headed.
By this logic PDAs are dead, calendars are dead, pocket calculators are dead, heck even phones are dead. But not really, they've all just converged into a single smarter device. We currently call it a smartphone, but to be honest a better name would be "pocket computer" or "pocket tablet." Heck, I spend a lot more time using my "phone" to read books, watch movies, listen to music and browse the web then I use it for making phone calls.