This, or something close to it, is surely the reason. Everything Apple does can be traced to a motivation to sell more hardware. (e.g. iTunes, App Store, iWork, Apple Maps, etc...)
Hardware and the OS are their secret sauce, commoditizing everything else (applications, services, content) is in their best interest.
Hardware and the OS are their secret sauce, commoditizing everything else (applications, services, content) is in their best interest.