I would hardly call making available an XML file with a list of songs and playlists, as means of interoperability with iTunes. Maybe you're confusing it with iPhoto, which actually does allow interoperability with various cameras and devices. Like iPhoto, Mac OS X's default music management application, iTunes, too needs to be device neutral (especially when it can be achieved by simply NOT blocking devices based on USB vendor IDs).
I think, this type of application behavior only makes Apple look insecure. People will still buy iPods and iPhones, regardless of whether iTunes allows syncing with other devices.