Google guidelines are common sense, it helps to know the technical details though.
One common sense guideline is not to allow your sites to become a platform for scams and spammers to use, this happens when you allow folks to comment spam your pages.
What if WPW quit watching things and spam botnets started posting online pharmacy links all day long here, do you think Google would allow WPW to retain their
PR or that Google trustrank would place value on this forum any longer ?