Historically, it's both, which is how we got here. The Xerox demo was definitely trying to make near-as-possible 1-to-1 correspondences because their entire ap

Historically, it's both, which is how we got here. The Xerox demo was definitely trying to make near-as-possible 1-to-1 correspondences because their entire approach was "discovery is easier if the UI abstractions are couched in known physical abstractions." UIs that hewed very closely to the original Xerox demo did things like pop open one window per folder (because when you open a folder and there's a folder inside, you still have the original folder). As time went on and users became more comfortable with computerized abstractions in general, much of that fluff fell by the wayside. MacOSX system 7, for instance, would open one window per double-click by default; modern desktop MacOS opens a folder into the current window, with the option to command-double-click it to open it into its own... tab? (Thanks browsers; you made users comfortable enough with tabbed windows that this is a metaphor the file system browser can adopt!).