Being a HN reader, you probably have enough experience with computers that the cognitive load of tasks like file management is basically zero. But for most people, even many people who use computers on a daily basis, the cognitive load involved in managing a library of thousands of files is much higher than that of simply plugging something in. Unless they have a particular motivation to favor the former, the latter is always going to be more appealing.
Of course, control is the reason Apple/MS don't also allow access to the filesystem on these devices.
iTunes and Zune make it much easier for the average consumer to manage a library of music.
Tell that to my dad and sister who deleted their whole collection of mp3s thanks to "iTunes making it much easier".
The latter gives you control, the former "just works" (usually).