Illegal Tying
Apple gets around the illegal tying because they do not sell the OS on the retail market. The OS you are buying in the store is an upgrade that requires you to have a prior installation on the Mac. So Apple does not sell their full OS in a retail box.
Sure you can "hack" the CD to create a full install but that doesn't count in the courts. So without changing the retail CD the only way you can buy the full OS is buying a Mac computer.
Paris cause she almost looks smart in glasses
Biting the hand that feeds IT
