Actually, I am not thinking about the interface at all. My point about being able to simply drag and drop the media is regarding how a platform like Maemo makes those files completely transparent; I don't really have to concern myself with what kind of audio they are, since they will probably work. I can thus export them from any app under the sun (drag and drop being a really nice way to do it, for an inter-process communication fan like myself) and expect them to work.

With an iPod, on the other hand, you don't just happen to use a manager app; you are stuck with that manager app! Yes, you can still do things in mass storage mode, but getting files to play when transfering them like that is another story, since they have to be just the right format. Inter-process communication is all about interoperability, where applications can easily integrate with each other on the idea that they share a common ground for how they work: files. With drag and drop simply carrying URIs as information, we can end up with an incredibly rich and flexible environment built simply on that simple concept, where if somebody wants something somewhere else he need only drag it there. (Unfortunately, while DnD is one of the most powerful, easy to implement and useful integration technologies we have, it requires a very strict and demanding movement, giving it a bad name and making it unfavourable for a lot of people -- particularly those with lower mouse sensitivity. We need drag and drop without the drag!).

The success of that system assumes that they all use the same system to access the media (gstreamer, for example), so that things actually work reliably when received. Otherwise, dropped media would often not be picked up, which would not be very nice!
When it does work, the advantage to DnD is that the weird concepts of actual files and their formats are made very transparent to the "end users", allowing people to use specialized managers as opposed to generic file managers wherever they please. Integration's cousin is choice, which is being able to drop in any software solution wherever one pleases without losing functionality. I, for one, like using my file manager for programming projects but I prefer F-Spot for photos and I would rather not think about how F-Spot makes a mess of my file hierarchy. Since both systems implement drag and drop very predictably, I can do that and easily switch between the two with ease.