The same way Apple would prevent the installation of OS X on non-Apple-branded computers: legal challenges against those breaking the "EULA".
One of the main points of debate is how successful such a challenge would be.
I took that as an invitation to think things through. If I got a letter from a corporation telling me that I did not have their permission to install the stereo that I quite legally, openly bought from them, I would just laugh and proceed to install the stereo.
Wouldn't you do the same?