What one simple thing is iTunes supposed to do? From early on it's been a multi-function program. It would be very difficult to pick out a small subset of features to point at as the core functionality of iTunes since from the early days it's been a music player, CD ripper, store, device manager, etc. Probably the last major new category of functionality added before Ping (which arguably is just an extension of the store) was video playback.
Music player + CD Ripper can be the simple thing it's supposed to do. Move the music and app store into a separate app. Move the device manager into a separate app. Move the social networking into the cloud.
