Low value posts aren't really 'spam' unless you have some ad in your sig.  The point is that a human being can manage to post five times in the newb section and sound like a real person responding to other low content posts.  A bot will flail trying to post in the other sections, because this rule is uncommon, and hopefully those kind of people that just move from forum to forum trolling for cheap amusment will prove too impatient to post five times and read the forum for a couple hours before having something to 'contribute' and thus move on.