Mossberg's got an interesting observation here, but he's missing a really important point: Apple's core profit engine is selling hardware. Amazon and Google make money by selling services and non-hardware goods.
Since Amazon/Google make money regardless of platform, they have an incentive to produce content for Apple's platform. Since Apple only makes a real profit if/when you buy their hardware, they have no incentive to do the same.
Since Amazon/Google make money regardless of platform, they have an incentive to produce content for Apple's platform. Since Apple only makes a real profit if/when you buy their hardware, they have no incentive to do the same.