The only thing proprietary about the new Macs is it uses the Extensible Firmware Interface instead of the standard PC BIOS. And EFI really isn't proprietary. It's a well-documented standard that PC manufacturers will likely be using in the future.
A "commodity" PC is OS agnostic
So is a Mac.
A Mac is designed to disallow running anything but an OS from Apple.
Really? You might want to tell that to Apple.
You seem to have fallen victim to common Mac myths.
Apparently I was mistaken. But the whole point of having the OS vendor control the hardware is to enable them to optimize the OS for a known and limited set of variables, and you’re going to pay a premium for that integration. Installing another OS on that platform effectively negates that advantage and the additional cost was for naught.