As an instructor, one must be able to perform, on demand, anything asked of the students. I've heard this lame excuse bandied about before and it still smells like crap.
It is policy where I teach that all instructors must be able to demonstrate ANY/ALL techniques taught at any time. I am never asked beforehand if I want to do a demo. I simply DO IT. How can anyone teach something well if they cannot not actually do whatever it is that they are teaching?
Bottom line, IMHO, is that instructors should always live fire in front of their class, if only to simply demonstrate the proper techniques in use! That should preclude any mall ninjas from reading an article in a gun magazine and calling himself a trainer. I apologize if I offend anyone, but at 10 yards, you should be able to pick which eye you are going to place the round.