Pot and Kettle, Maybe?

Webforums are kinda like this. Not sure what it is about them that makes forum admins and moderators so up-tight about everything.

Only web forum I've ever visited that wasn't like this was also the least interesting one.

It may be the case that mailing lists aren't like this because the medium is less confined. You can exchange funny e-mail with people off-list but while using the same interface so you may feel like you can get it out of your system without disrupting the general conversation.

A webforum, by contrast, puts all stuff where all people can see them. Any random, silly post can appear in search results and thus easily be read out of context so the entire topic could be misrepresented.

In order to prevent this, moderators get hyper-sensitive about being on topic… to the point where they can't even laugh at a genuinely funny, harmless distraction.