I was taking another look at this question and Ólafur's comment. It's a very good point: If the best answer to a question is close but needs some example code or other clarification, editing it makes sense. Most users don't have enough rep.
Here's my proposal: why not give the asker edit privileges to answers on his own question, or at least to the accepted answer, at a much lower rep (250? 500?). You could also let the asker append to, but not edit, the accepted answer, like this:
Is it plugged in? Loose power cords are the cause of many no-start problems.
It was, in fact, plugged in, but the power strip it was connected to had gotten turned off. Maybe the cat's fault?
…This would let the asker respond with code blocks, blockquotes, and other useful formatting that can't be used in comments.