Thinking about the evolution of community rules and how they start from don't be an asshole
Don't be an asshole: Fine for tiny communities with one person in charge who determines assholes or not. Likely a community based around that person, so disagreeing and leaving easily comingle.
Don't be an asshole, here are examples of assholes: The community has had people who toed the line, and caused a fuss before being banned about what exactly an asshole is. Specific things had to be written down and are now considered 'asshole behavior', where before it was assumed you just didn't be an asshole.
Clearly delineated asshole categories, determination of asshole is now multiple people's responsibilities: The community has grown, and either no longer is based around a single person, or is too large for that person to moderate themselves. Now there are rules and guidelines about who to consider assholes, and how to handle asshole tiers.