Action, Treasure and Night have rules.
Duration has several rules.
Victory has a rule, which is that the victory points on it are counted at the end of the game. The same with Curse.
Attack, Traveller, Command and Gathering have no rules, but are referred to by cards. (The setup rules are for Page and Peasant, not Traveller.)
Reserve has no rules, and no cards refer to it.
Looter has a setup rule. Sure, we could theoretically get rid of it. We would have to say the that Ruins are included if any card that mentions Ruins is in the game. We could get rid of Doom, Fate, Heirloom, Zombie and Clash the same way, since they only have setup rules. But, you know, they do have setup rules, and for good reasons.
Reaction has some rules, for instance the one I mentioned, that a Reaction in your hand can be resolved several times when it triggers. The other rule is the complicated one about getting a new chance to resolve a Reaction if another player did something. Okay, those rules are not technically limited to Reactions, but in practice they are, and they would be even more difficult to phrase without using that tag.