I fully understand your point here Frank but I'm not sure I'd go that far (at least from my standpoint). For those of us who have much much less experience, it's very educational to hear the discussion of all the possible causes of an accident, speculative or not, as long as they're realistically possible.
For example, when I read an accident thread and see you positing that the cause may have been X, Pete says "I think it was Y," and then PfcAj says "Maybe but Z seems more likely to me," then I know damn sure to not do X, Y, or Z, since regardless of whether any of those actually caused the accident in question, more experienced divers whose opinions I trust are telling me that they may lead to the same outcome. And in many cases, I hadn't even considered the ramifications of some of the actions being discussed.
I know that you're actually talking about the usefulness of these discussions as they relate to providing feedback for improving training organizations but I just wanted to point out that all things considered, speculative discussions aren't entirely worthless.