The rules can't actually be dictated by the miners - e.g. they can make invalid blocks but clients won't accept them. They can censor transactions, though that

The rules can't actually be dictated by the miners - e.g. they can make invalid blocks but clients won't accept them. They can censor transactions, though that can only delay it until a non-colluding miner includes it. The Bitcoin XT chain fork is a bit different in that it explicitly tied itself to miner voting. That's not necessary, you could really tie it to anything.