You are therefore defeating your own argument. You initially say:
To use x86 processor you must use the same hardware arechtecture (Motherboards, rams ... etc)
Then you say:
Xbox is a closed system, which means special GPU, special drive ... etc
No way to make it use any graphics card thru PCI/AGP bus and general IDE connection and don't be able to run the os for it with standrad system
Meaning you agree that you can
use an x86 CPU in a system which is not fully compliant with the 'Windows Compatible' PCs that you say 'must' be able to boot into MacOS when they release an x86 based system.
Apple can release a unique piece of hardware based on an x86 CPU and thus stop different hardware configurations being able to use the OS.
As a side note, I am playing devil's advoate, as I totally expect it (MacOS x86) to be hacked to be able to run on ordinary windows whiteboxes, at the very least through a VM transparently using the CPU or, ideally, being fully bootable.