Simplicity was one of the things that sold me on the iPod. My previous Nomad Zen had an awkward interface and it only worked as a removable hard drive when you had the proprietary Creative software installed. Granted the iPod needs iTunes to sync with the PC, it's a terrific program in of itself and it makes it really easy to sync and organize all your music just by plugging in the FireWire cable. I can buy most of my songs right in the iTunes store and I can do that within the same application. Sometimes "keeping it simple" is the best marketing platform, and it has obviously worked out great for Apple.
I know there are MP3 players out there now that "do more," but that brings me back to reason I bought an MP3 in the first place. I wanted a portable music player. What do I care if it has built-in PDA functions and other toys? It's just like my theory on cell phones. I buy a cell phone to talk, not to play silly video games, snap pictures, and balance my checkbook. I have a computer and camera for that! Bah!