Not sure I'd call myself a fan, but I was an engineer on the Xcode team for a decade. The answer to your question about coupling is "ease of testing and coherence".
Prior to Apple, I was a senior engineer on the dev tools team at Microsoft. We did the same exact thing wrt full-release testing and vendor hardware.
I'm not saying I agree with the way either company handles coupling, lock-in, etc. but if you don't think that the Windows UI is coupled to ring-0 you don't understand how it works.
Why should OS presentation be tightly coupled to kernel version?
Or why should it even be coupled to the vendor of the hardware?
And you can ask the same question about content filters, app stores, ...