Ray- I've had the exam explained to me by PH's that have taken, and passed it. I'm certain I can't do it justice when describing it as someone that has taken it so I look forward to hearing from them as well.
From my understanding, competency with your rifle is just one, albeit important, part of the exam. You are also graded on tracking, guiding, field dressing, cooking, knowing the laws, etc. Basically, having the ability to host and guide your clients in a safe and legal manner.
The great PH's inspire confidence that we, as clients, will have a fantastic, overall experience and taking the shot is just one small part of it.
Again, I'm not the expert so I'm very willing to learn if I have it wrong.