I'd say it's more like proprietary hardware built with commodity components. A "commodity" PC is OS agnostic. A Mac is designed to disallow running anything but an OS from Apple.
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.