The other interesting, and contradictory note to a previous post:
Eventually there seemed to be only one reason to buy a rival device [to the iPod]—it was cheaper. But it turned out price wasn't a deciding factor for most people. Customers chose the pricier iPod because it offered a lot more, not to mention because it had become a fashion statement.
I'd probably argue it was the integration with iTunes (both the store and the software which provided easy ripping) and support for MP3, which meant it just worked, that were the main factors, plus big market share which meant personal recommendation from friends and lots of add-ons, such as speakers and docks.