I agree. The whole libel argument is a joke. No way is the operator of a free message board going to be held responsible for libel by something a message board participant posted, unless it could be proven that the board operator was somehow a willing party in the posting of the information, or if that site kept the information up even after finding out the information was false.
All Jon would have to do is post a disclaimer regarding information posted on the site and perform routine monitoring.
Like the last post said, all this should be moot, because Jon is free to run his site as he pleases. That is a sound argument, that doesn't need to be sullied by the ridiculous libel talk.
Okay:
On second thought, Jon might actually be considered a publisher instead of a distributor as he does publish original content and also has posted rules about posting. Still think would fall under the distributor guideline for the message board, but it could at least be something that an opportunistic attorney might try to exploit.
The best way for him to avoid being considered a publisher of the message board is to stay out of the discussions, not claim to be an active editor, and leave his articles/posts/blogs in other areas of the site. Therefore, he could claim the message board is separate from the rest of the site.