'PC' ('personal computer') is a general purpose computing device, based on the original IBM architecture. The point is, it was never tied to any particular operating system.
Any attempt to 'tie' the hardware to a proprietary OS can be met with a legal challenge on these grounds. So, regardless of what manufacturers would like customers to think, it is possible to obtain an OS-free computer, even if it entails refusing an EULA and getting a refund for the unused OS.
Many people think this argument applies to Apple, too. But that's a mistake: Apple computers are not marketed as 'PCs'; and their computing system, from hardware to OS, is Apple throughout.
Microsoft works with PC manufacturers to pull off this anti-competitive hoodwink on an ignorant computing public. If it were tested properly in court, the whole corrupt practice would be torn to pieces.