I believe they have other, closed source, anti-spam measures. This might be the reason, but if it is 'tis a silly reason. If I understand correctly, it means th

I believe they have other, closed source, anti-spam measures. This might be the reason, but if it is 'tis a silly reason. If I understand correctly, it means that if 75% of people like a post, and 25% dislike it, that means it has a 25% chance of not being successful because the first vote is negative. Overall, this measure is effectively lowering the quality of all content on the site.