Yes you are right as far as it all being relative to the chance of a dud versus ammo loads. However the point I am trying to make that maybe I am not being clear about is how the 'duds' affect 30mm planes more because of the method of properly firing in a tater plane.
A proper 50 caliber gun solution (lag pursuit) will yield continuous guns where a barrage of bullets will saw a plane in half. It might be as many as 10 hit sprites in a centralized location to make a part fail. When you work with this gun solution, a couple duds mixed in don't really make a difference, as you simply fire on target until the wing saws off. No big deal if it takes an extra .5 seconds.
The tater is different though, as you work for crossing shots. With these angles of attack you are working a gun solution where the enemy plane will zip by your cockpit at a very high rate of relative speed. Firing a barrage of taters out in front of his flight path will usually only yield one tater connection if you are lucky, due to the slower rate of fire and your enemy's relative crossing speed. So if you fire 5-7 taters out in front, and the one tater that is to hit him is a dud, not only do you lose 10% of your ammo, but you also missed out on the only gun solution you had there. There's no makeups once you see it is a dud, it's too late to fire again, he's past you.
I know this explanation might run somewhere on the KRUSTY scale with you, but I'd hope it makes sense after this explanation.