There's a reason I used Nintendo for my video game analogy. They will never license Mario, Zelda, or Pokémon to the other console makers (because of they did, they'd go the way of Sega and Atari). They also used proprietary connectors and game cartridges/disks up until recently (the disks are a standard size, the connectors are still proprietary). PlayStation uses standard inputs like micro USB. PS and Xbox have also always used a standard disk size. But you still can't play those disks in the other system. Sure, there are third party game makers, but they still have to make and sell separate disks for each platform. For my analogy, the record companies sold different music files for each online music store (iTunes, Napster, Windows Media Player, Real Player, etc). Plus what about PC gaming? A CD-ROM or DVD-ROM could be played in any computer running the appropriate specs and OS.
My point is that Apple is not the only company who tries to create a walled garden. They just have less of an excuse. And honestly it's not relevant anymore with the removal of DRM. I can buy music from Amazon and easily transfer it to iTunes and sync to my iPod or iPhone. And then there's Spotify which takes the music store away from the hardware or software maker altogether.