Zaikesman,
"I agree that quick A/B's often don't reveal nearly as much as there is to hear."
None of the threads on Audiogon that I read, including this one, or the Stereophile article on DB testing contain an explanation for your statement that is supported by scientific data. Until some neurobiologist/psychologist becomes interested enough to devise an illuminating experiment, we can only conjecture.
"The solution in my experience is not to throw away A/B's altogether, it's to keep doing them until the finer differences emerge, which they do if you have the determination and patience."
I agree with your solution! Perhaps (Oh,Oh. Another conjecture is coming up.), repeated A/Bing results in the formation of new neuronal connnections or the strengthening of weak ones that facilitate the discrimination of finer differences that were perhaps (!) previously masked by "after-images":-)