“us”? For me, DT behaves like most other apps: one tab, one document. The Finder is not different (one tab, one “document”), but its documents are folders. And you can, of course, display folders in different ways. Which is difficult for a single MD document (for example).
Also, your statement that “tabs basically contain an instance of the app” (in the other thread) is plain wrong, at least for browsers. Tabs are sandboxed against the app, and for good reasons. And they only give you a single view of a single document. Putting windows in tabs is (for me, not for “us”) mixing the metaphors. Why not use differently setup windows side by side?