It's just a question of the degree of lock-in. And Apple is a master of lock-in: purchased apps for iOS and Mac OS X don't work anywhere else, FairPlay prevents movies purchased from iTunes from working elsewhere, AirTunes is locked via DRM to iTunes, things like MagSafe are protected with patents to maintain their profit margins, and so on.
It's just a question of the degree of lock-in. And Apple is a master of lock-in: purchased apps for iOS and Mac OS X don't work anywhere else, FairPlay prevents movies purchased from iTunes from working elsewhere, AirTunes is locked via DRM to iTunes, things like MagSafe are protected with patents to maintain their profit margins, and so on.