Making a garenteed drop for things like that should simply be common sense. It is basically garenteed that at least one person will never get the drop no matter how many times they try. It is the basics of statictics. Ever though it is extremely unlikely, it is garenteed that someone will win the lottery, except the lottery in this case is losing a 1/10 chance 100+ times. Bungie is just either lazy or dumb.
Agreed, leaving it up to plain numbers to decide when it drops for someone is a huge mistake for something that takes up people's time / effort so much. They need to have added percentage for the drop to increase per completion ages ago. People who are working full time and balancing life, will never see these weapons otherwise! Like we don't want to be going back and running old(er) content when the fresh new raid is out, ya know?