Erica, you are right, it is of course my preference. However, I understand that all features are based on different preferences which you may/may not use. E.g. somebody is not using tags or colors as it is not his/her preference. What I derive from the fact the both Omnifocus or Things enable this feature (quickly move through the document list using keyboard) is that many users share it.
Just to be precise - I was replying to butlermatt suggestion as how to implement filepane navigation (if by switching focus + normal moving by arrows or by special shortcut)
To my point 2): What i described was not meant for the situation with closed pane list, but with open pane list. Even with open pane list I used to be confused about where I am (what part of the window has focus) in omnifocus, because it implemented the functionality as butlermatt suggested (switching focus from main document to sidebar instead of just using shorcut to move through sidebar) - I was not sure where my focus is because both your current document in document pane is greyed (so you know which document you edit) and the current line in the edited document/list is grey (for the same reason). My problem was that you were not able to clearly say (without moving mouse or arrows) what part of the window has focus eg. when I switched to the app window from other app. Which was not the case with Things, as it implemented the feature the other way, without switching focus.
(I was replying to butlermatt suggestion, not to your question about what to do when pane is closed. Still I think that document navigation shortcuts make sense also with closed pane. In my opinion, the situation is similar to going back to history - you also do not remember always how many exact moves you will have to do but you know that three or four moves away back in history, you will see your document. It is the same with navigation (with closed pane): you know that your document is somehow two or four moves down, so you just push the shortcut more times until you see it.)