The following system sort of takes care of that. By posting intelligently, holding off on the swearing, etc., you attract followers who trust that you'll keep it that way. If you started posting shock images under innocuous titles or something, you might not get banned because people don't really get banned, but you'd lose all your followers quickly. Slightly like a shadow ban now that I think about it. So this is why hubski doesn't have/really need a 'rules' page.
This makes a lot of sense, and is promising to me. I really enjoy how natural this site feels. It just feels like a 'normal' thing for user-content sites to have some sort of general guideline. For example, what is the #askhubski tag for? There really is no straight definition of a lot of things. (Most are self-evident, but I'd still urge you to think about it)