Ah, this seems to explain what I have been seeing with people posting a very quick one sentence answer and then expanding that answer through edits.. Might this particular gem be a bit of a way to game the contest system?
If the user expands on their answer, then the asker gets their problem solved incredibly quickly, which is awesome.
If not, the answer is likely to be downvoted (or deleted if it's not a real answer). In past contests negatively scored posts didn't count, I would asssume that's the case here as well. If not, I think it should be!
Posting the short answer, without all the extra details a person might want to know and then expanding it in a series of intelligent edits is a very responsible thing to do.
It gives the asker a quick answer, as quickly as the answerer can, and it also gives the complete answer, as quickly as the answerer can. The poster is being maximally helpful, and is doing a little more work to be helpful. It's a good thing that it's rewarded.
That said, I agree that if you see someone gaming for "first!!!!!!11" with a placeholder "answer coming soon" that isn't actually an answer, the best thing is to give it a downvote and a comment, that'll teach them not to rather quickly (and anyone else who sees it happening, as well).
It is certainly not about the speed at which you answer, but the quality in your work. If they go back in and provide a quality answer that is better than the other answers then they deserve to get the upvotes. Some people just like the reassuring placeholder that says "Hey I'm going to answer this just give me a minute....jeeze"