As I've mentioned, written rules make people intent on causing trouble reading through them, quoting them, and thinking they're right because they think they've found a loophole. Communities are made up of people, who are social animals. If they're going to make mistakes, some text won't change that. If they're going to cause trouble, they'll use anything they can. The social game on the internet is so based on personal freedom that rules are almost always ignored and/or used wrong.
Furthermore, if users want a rule page so they can just link it to new people who ask for it, we would decrease the amount of real interaction that goes on when you have to explain how an organism like a community works. It caters to laziness, and most don't read it anyway when linked up.
@Naesala: One mistake does not a moron make. I've seen much worse cases of public accusations, and I don't think it's a personal issue that some of you did. In fact, when someone's already done it, it's easier for other people to do the same. That does not change the nature of the mistake, but a stupid mistake does not equal a stupid person.