The fanboyness here really is hysterical, and I'd like to see someone answer this... to help out, I figured I'd pose a few questions (with the assumed fanboy answer in parentheses).
1) Is it OK to run OSX on a Mac Pro? (YES)
2) Is it OK to run OSX on a Mac Pro if I had to swap out the ram, hard drive, and graphics card? (MAYBE)
3) Is it OK to run OSX on a Mac Pro if I had to swap out the motherboard/processors with something faster than it shipped with? (NO)
4) What if I pulled everything out, but still kept the Mac Pro case? (NO)
5) You mean it still isn't an "Apple branded" computer as specified in the EULA? (I DON'T KNOW!!! LEAVE ME ALONE!!!)
In all seriousness, I'd love to see you all answer these questions.
I'll meet your challenge.
1) Yes.
2) Yes.
3) Yes, unless by doing so you inevitably render it a different computer, thus breaking the OS and having to hack it like a Hackintosh. I don't know enough details to know whether this is the case.
4) No.
5) That's right. An Apple computer is one sold by Apple. Pulling everything out but keeping the case amounts to casemodding a regular PC with a Mac Pro case.
This is what we in the Philosophy department like to call the "Ship of Theseus" scenario. Theseus has a ship of wooden planks. Every single plank, over the lifetime of the ship, is replaced, but only ever one at a time. At what point is it no longer the same ship?
Answer: It is always the same ship.
Objection: But what if someone saves all the planks that have been replaced, and rebuilds the ship to the same plans with every plank in exactly the same position? Doesn't this ship have as much claim to be the "original" Ship of Theseus as the one from which its parts come?
Answer: No. A ship is not merely the sum of its parts; it is also their functionality.
The same applies to a computer. If an individual computer part (I'm talking functional parts here, not the case) is replaced, but the computer runs basically the same, it is of course the same computer. (Changes to specifications don't matter; they're like using a different timber in the ship example.) The computer retains the same
functional identity. If every part is replaced at once, it does not have the same functional identity, because you are either replacing it with the entire innards of another Mac or you are forced to hack it in order to run OS X. You wouldn't say "Theseus is replacing every part in his ship at once, but it's the same ship" you would say "Theseus has a new ship".
Putting a different computer's insides into a Mac Pro case does not an Apple computer make. If Theseus sells his old ship, buys a new one, and gives it exactly the same paint job or markings on its sails, does this make it the same ship? Of course not. The case, or the paint job, are not functional components. This is why casemodding a Mac beyond all recognition does not rob it of its Machood, and putting a PC inside a Mac Pro case does not make it a Mac. If a PC is modded to fit inside a Commodore 64, is it then a Commodore 64? Of course not. What if it is equipped with an emulator? Nope, still not a C64. It is functionally
equivalent to a C64, in that it can do anything a C64 can; but functional equivalence is not functional identity.