The code, at least the 2006 CEC, offers no definition of what is and is not a closet that I am aware of.
I am not sure how 26-712(f) helps to shine any light on this issue.
The question is, at least in my mind, when is a walk in closet not a closet and is in fact a room off of the bedroom. Maybe the number of square feet of the floor of a closet should be the guideline.
Interesting...