> The desktop is kind of weird, in the sense that it's prime real estate but, at the same time, there's an expectation that you shouldn't put too much stuff there,

If we go further into the metaphor of a desktop, there would be sections for tools and sections for pending work. The inkwell versus the blotter, if you will.

But then, well, what difference is there between a designated permanent zone of the desktop for non-tools, versus a regular window showing some contents of a folder, which the user has chosen to position above an empty area?