The big reason why I see people buying one of these is to replaces multiple tools to combine them into one. Which is what we all want eventually. Less clutter.
It's also simple. The interface is intuitive and the device has no moving parts. What I liked most about the iPod wasn't it's technology, it was that I actually *used* it on a daily basis for productive things. Most people don't think in terms of technology, they simply gravitate toward what serves their needs.