Doesn't Apple pretty much own their whole stack? You mentioned XNU, which they made...

Their CPU, their boards, their firmware (presumably), their OS[1], much of the perhipherals are theirs, too.

Lots of companies try to emulate Apple, but it's very hard to pull off.

[1] Yes, they use some parts from Mach and FreeBSD in their OS, but the amalgamation is theirs, and they support and change the whole thing as needed.