You can't run a legit copy of OSX on anything but Apple hardware. It's not for white-box systems and technically isn't legal as it's against the terms of the software license.

That's not to say it doesn't work, some systems are compatible enough to install/run it but it's a specific hardware subset that has drivers. Regularly you also need a hacked version to put in the boot loaders etc for non-EFI systems (Macs use EFI, PCs use a BIOS).

They do it because it means they don't have to manage drivers/support for a whole bunch of shit. That's always been the reason Windows sucks. Windows of itself is okay - it's trying to keep compatibility with every bit of hardware and software ever made which fucks it up, and as soon as MS removes support for anything people cry for blood.

By keeping everything to a limited little supportable space, it means you CAN make a system where pretty much everything just works, especially when you're responsible for the hardware too.