I never noticed this practice on stackoverflow or serverfault, but I noticed on superuser that some users will answer a question if a placeholder that either barely or does not answer the question it was in response to. Several minutes later, the user will then edit their post to answer the question and incorporate other answers. This seems like a blatant abuse of the system.
I understand that The Fastest Guns in the West is considered solved, but doesn't this kind of abuse seem like a response to at least the perception that early posts are accepted and up voted more often?
In short, is it an abuse of the system to post placeholder answers to a question and if so what can be done about it?