"How is that even a function of the operating system?"

My statement was provocative, I guess. This is like a Harley driver asking if a Yamaha is a real Motorcycle (is it?).

Backup is not a function of the operating system, but the key question is whether software is available FOR the operating system. Could be even an issue of bios, but who cares except theorists?

You always buy a package.

Yea the problem is the legacy PC BIOS which relies on real-mode boot sectors. EFI firmware has code to read file systems which makes this much easier, and PCs are finally beginning to have it too.