This is because places where typing in text that contains spece should not be considered as a "menu" by DF, it should be considered as a text box of something.
Example:
In windows, a button is not a popup window, and when chaging the name of a gfilename in explorer it is quite clear by the highliting that you are "just inside this small zone here", so the commands are content sensitive. For example, right-arrow in file explorer meant "go right one column of files (if my view has multiple columns of course", but when I'm editing the name of a file it becomes "go right one character". There is absolutely nothing wrong nor "unconsistent" with that. A text entry box is simply NOT a menu. DUH.
Having to choose BETWEEN spacebar *or* ESc is also a moot point. That would be the same as microsoft forcing its users to choose between either
hitting F4
*or*
Alt-f+x
*OR*
Alt+arrow keys until exit menu item is highlighted+enter
*OR*
clicking file then exit with their mouse
in order to use windows explorer, but ONLY ONE of these methods. Multiple intuitive ways to enter data does not necesseraly mean an unconsistent interface.
So I vote for having alternate keys. "Important" keys (spacebar, escape, arrows, enter) should ALWAYS default to the most intuitive behavior, never be "oh, that is now a dead key because of some setting somewhere, exiting is done through that OTHER key over there".