In taking a closer look, nothing nefarious is going on. Since it's impossible to know someone's motivations for voting, I am going to err on the conservative side and assume that people are rewarding good posts only on their merit. However, with badges in play, there is always a chance that people will "hunt" them. Good content should always be ...


It looks that the threshold is 10 votes, as jonsca mentioned in a comment to the question.


Looking at only the numbers of 'New Users in week' after the change they seem much more variable than SO but average out to be slightly declining, with a slight recent upward trend:

Only top voted, non community-wiki answers of a minimum length are eligible