Unfortunately it only took a few years for Apple to start sliding away from their own guidelines, and Windows was always less rigorous to begin with. And then the Web came along and blew the state of UX back to the Stone Age. Sigh.
The Mac is great and all, but I've used a 1984 Mac and I don't think I want to adhere to a guideline centered around running a single fullscreen application at a time.
That was more of a technical limitation than a design guideline, though guidelines may have been constructed around that. Many of the things those guidelines point out are still applicable today by virtue of the fact that Mac has stuck with its "Finder" system of interaction for 3+ decades.
Unfortunately it only took a few years for Apple to start sliding away from their own guidelines, and Windows was always less rigorous to begin with. And then the Web came along and blew the state of UX back to the Stone Age. Sigh.