your arguments stand up with current visual technology (monitors = a small 2d window into "data space") but not neccesarily with technology that is not yet in common use.

Look around whatever room you are in and see how much data is intuitively organized in a three dimensional space. I can point to any of a hundred books on my shelves, DVD's by approximate location, files of financial data, etc. The human brain has an amazing ability to organize objects using spacial relationships. This ability is part of what makes folders, desktops and menus a useful and usable means of organization instead of or along side simple file lists. (I intuitively know the "physical" location of the couple clicks it takes to get to all my commonly used files and software. This is done without even reading the text and tends to be quickly relearned when I change things on my system)

But, all these are very limited by display space and lack of depth. I think that upcoming technologies will make more use of our brains spacial abilities to expand the "area" usable to organize data in all three dimensions.

One final thought is that tabbed browsing is somewhat of an analog to having a third dimension added to a browser. There is one layer "on top" with all the rest underneath.