I think you don't see negative reports allowed because it is often presented in a slanderous or very immature way. If someone would post "negative" comments in a mature way, it might be allowed.
Plus, so called bad customer service is often subjective, where as good service is obvious, as in Brent's case. I usually chock up bad service threads to a lack of respect on the customers part, or they're pullin the three year old card of "I want something, and anything but constitutes bad service".