You could make the argument that if the implementer has to know anything about why the protocol or crypto works then the spec is poorly specified.
Certainly it helps to have a minimum of appreciation of the other parts of the domain, but I think you greatly overestimate how important that is for the kinds of problem we've been seeing lately.
In any other field, I would agree with that assessment. In the world of crypto, with side-channel attacks on the sound of your keyboard as you type, I think that having domain knowledge is essential for any implementer.
You could make that argument, but I will join with mehrdada in disagreeing with it.
It's possible that more vulnerabilities are caused by programming errors than by protocol misimplementation, but the latter do happen and are just as bad.
