Okay, let's put it this way.
If the probability of failure of the DIN O-ring is *zero* (to a reasonable approximation) and the probability of failure of your basic hunk-of-metal DIN-reg-to-yoke-valve adapter is also zero (again, to a reasonable approximation), then the probability of a failure between the reg and the valve is the same whether you're using an adapter or having the reg changed to yoke. Basically all the failure potential is in the little yoke O-ring.
The only thing that leaves, then, is the geometry. If the yoke adapter makes the reg bash you in the back of the head (or so), converting the first stage to pure yoke will set it rather closer to the valve opening. On the other hand, if you can already dive without the discomfort of being bludgeoned by the reg, there is no reason you should convert it to pure yoke, as DIN-with-adapter is far more flexible (since it can be used either as DIN or yoke).
(Oh, and incidentally, when dealing with loud breakfast kitchens, you have a raucous din with lots of yolks, but when dealing with scuba regulators, you have DIN and yoke -- think of the oxen, not the chickens.)