I had actually never put it into words before now, but that makes a lot of sense, and it actually accurately describes how I see my screen.
To me, the OS taskbar is "higher" (as in, closer to me) than the application window title bar, which in turn is higher than whatever controls are in the application itself (think Firefox back and forward buttons, URL bar, setting menu etc), which is itself higher than whatever website it is currently loaded. And even more than this, my brain perceives the website to be "deeper" inside the screen than anything else.
Even right now typing this, the text area to me is "dug" inside the HN, making HN feel closer to my eyes than the texarea for the reply.
I wonder if that's experienced by others as well.