SO doesn't do anything to make this a better option really. I mean, you can always delete your answer if it goes negative. You can even get a badge for it. (http://stackoverflow.com/help/badges/38/peer-pressure)
This is annoying for people answering the questions too: what should I do when I know the answer but it's already in the comments? Duplicate and rake the points for it? Leave it be and leave the question as unanswered?