You know you raises an interesting question for me, especially following Apple leveraging their unique access to the OS with their latest opus, the external battery hunch-pack, over their competitors products, and charging a premium for it.
This restricted access to the OS to enhance its own products, reminds me of Microsoft bundling IE with Windows, giving it exclusive access and tighter integration with the OS, that competitors didn't have.
I have to wonder if this isn't going to become a problem for Apple sooner rather than later. Certainly they can't be accused of having a monopoly on the smartwatch market, but their domination of the mobile phone market is getting up there. And once they are shown monopolizing certain OS features to the exclusion of their competition on a dominant platform, it won't be hard to apply to other products where they are doing the same thing, even if not a monopoly.