Now i am not expert by any strech of the imagination at all, but i've talked to a couple of friends and i think it may be because the base architecture of a lot of the CPUs both Intel and AMDs is the same ( ). i think this may be it, with the whole CPUID instruction as well. i haven't had time to look at this document yet(i've only just seen your post) , but i think it may help: http://www.intel.com/Assets/PDF/appnote/241618.pdf (cortesy of Aryan)
If get time i'll read it and see.
Do correct me if im wrong, as i say i really don't know THAT much.
Hope this helps someway at least i tried