Yes, there's probably some Gauss thingy in there.
But my question is, if all the public rating does is to demonstrate the laws of probability, will it actually be of any help to people browsing the site? It certainly wouldn't be to me...
I don't think having ten different grades would solve the issue, though; even the five we currently have aren't really all used: 1 isn't used at all at the moment (which makes sense, of course, because we don't really want to add bad games, do we?) and 2 is only used about five or six times (two or three of those are in public ratings).