Comment by ThrowawayR2

When IBM lost control of the PC market when Compaq and other clones started coming out and their proprietary PS/2 PCs were rejected by the market, the power to define what a PC was fell into the hands of Microsoft, who still holds it today through their Windows hardware certification program. It is Microsoft who is keeping PC hardware open, albeit probably more because of fear of more anti-trust scrutiny than any altruistic motives.