In order to get the best comments and have the best community, there must be rules in place to inspire and also allow editors to weed out the bad ones.
Image from here.
… flagrant attacks on other commentators, staffers, or interview / review subjects, particularly aggressive, insulting posts with absolutely no other point to make.
… offensive commentary on interview / review subjects, including but not limited to ad hominem thoughts on how they look, how they might smell, and exactly what you’d like to do to them in the sack.
… racist, homophobic, or sexist remarks. Don’t assume that everyone else gets your sarcasm, irony, over-the-top tone.
… blatant trolling.
GawkerMedia’s rules are located on their legal page. They are generally very similar to the AV Club’s. However, the site goes further to explain how a comment becomes part of the public conversation on the site and inferring that a commenter should think before she posts.
So if you want to say something that you will later regret personally, it is advisable that you use a username that does not identify you. We cannot remove your comments simply because you have a change of heart about making them.
Reddit is open source so part of their commenting policy is a series of codes used to comment. They do have rules posted on their site, much of which links back to their FAQs. For a site that has faced so much trouble due to their content, they have a lot of rules.
Since The Awl was started by former Gawker editors, they have a similar legal policy. I believe that because of their content and readership, the community is self-moderating and does not need strict rules.
Image from here.
Not every site wants or needs moderators, people who read comments and mark them as spam, offensive, etc. Many smaller blogs self-moderate the comments, which often is a job unto itself.
Reddit has an extensive policy about moderators (and even a policy for moderators). These folks are in charge of certain reddits and have power to create and edit all of the information associated with the reddit, as well as manging comments and making sure they are within posted guidelines.
This is a great little resource full of tips for crafting a good comment. [warning: site plays video and music upon entering]