And how is that use-case unsupported on virtually all other operating systems?

One of the nice things (again, IMHO) of the Windows concept (and Linux, and BeOS and <insert any other modern OS> for the most part) is that just because you happen to have a window in focus doesn't mean that the principle OS menus need to completely reconfigure themselves for that one app. The functions of the thing you are working on are supposed to carry around with that object.

Under any other possible metaphor, what the Macintosh operating systems have done is madness.

>In the physical world, I mix and match media as suits the task, and the Mac mimics that. I don't fill my desk up with a notepad, then hide it and take out a calculator, then hide it and set up my easel.

This is the wrong metaphor. The metaphor Apple is using is like separating the pedals, gear shifter and steering wheel from your car, the doorknobs from your house and your office, and all the buttons from your calculator and throwing them into a toolchest that you have to carry around with you everywhere. Whenever you encounter something you need to operate, you open the appropriate drawer in the chest and operate it from there. Need to go get some beer at the convenience store? Open the 3rd drawer and drive your car from inside the drawer. Need to get in your house? Open the doorknob drawer and turn the right one clockwise so your door pops open. Need to use your calculator that you have out? That's the fifth drawer down on the right. Try not to make a mistake while bending down hitting keys, and then bending back up to see if the display on the calc is showing you something you want. Of course it's an Apple toolbox so it's all aqua-ish and shiny with rounded corners and a permanent lens-flair, and it's context sensitive so the right drawer "just opens" at the right time so it all appears to "just work". But it's annoying as all hell.

The interfaces to the device you are intending to operate should be part of the device you are operating.

The Macintosh Operating systems have always operated under the assumption of single app focus reconfiguring the toolbars, with clutter from unfocused apps taking up the visual space. I can't even count on all my fingers and toes the number of times I've closed a window in an Apple operating system, but not the App, and thought I was working with an app that was in the background that just happened to have a very similar toolbar - and got supremely frustrated that I couldn't bring that app in focus or do some operation from within the toolbar for the app I very clearly was looking at (and the only one I could see with windows on the screen. The disassociation of tools (methods) from the thing that you are working on (objects) is not only a poor abstraction, it's a usability nightmare.

Right now for example, I have my browser open in one part of my screen, a word processor in another, and two file browsers on another monitor. Nothing in the design of my OS is preventing me from copying and pasting from one to the other, or even dragging and dropping items or selections from one program to another. But my OS isn't trying to reconfigure itself to support whatever app happens to be in focus at the moment. But if I want to avoid distractions from the other apps, I can full screen any one of those things and it really is full screen, I won't see anything else on that monitor but that app. On Apple Operating systems it just sorta kinda fits it as best it can, but if the aspect ratio is not quite right or something I'll see other apps hanging out over the edges of my window.