I understand this rule and for the most part agree with the wording.
But at what time will there be some responsibility placed on each bowler to ensure his pins are correct before he throws his ball. This might mean if it was determined a pin was missing, you would be lucky it wasn't caught. But what if there was a penalty for not making sure all pins were present? If you got a zero for the ball if it was determined you made a delivery without all the pins, would you check to make sure every time? I know I am playing devil's advocate, but I hate it when someone from two lanes over has to tell someone he has pins missing because no one pays attention or even cares. I have seen many times people through a fit because you are trying to get their attention. Or after someone throws the ball and you tell them pin was missing, they have to get 5 others to agree because they don't want to lose their strike.
Anyway, that is a thought I have had before.
I am not a pro-bowler, but I do play one on BallReviews.com