The reports that some mods have heard indicate that spammers simply ramp up their spam to get over the threshold, or simply post ten legitimate comments to avoid early detection.
A member (now former member) was busted today who started out posting legitimate responses and then all of a sudden the posts turned into 100% spam and unrelated comments.
Spammers are persistent. A 10 post threshold would not stop me if I believed that the signature links would benefit my sites.

