There's no difference between a Minecraft server implementing moderation policies and an MMO implementing them. The self-moderation we're talking about would be on an individual level.
Moderation on Minecraft servers are done by admins, just as it's done on MMOs. Both controlled by a central entity. What is the difference?
The people appointing moderators are part of the central entity, unless you mean that the trolls being muted also have a say in it. Show me one such server that is not a tiny one with just a bunch of friends, where moderation is not needed anyway.