* Weapon and armour materials come in ladders. Leather is at the bottom; daedric is at the top. Immunity to Iron confers immunity to any lesser material. Since only leather is less than iron, and there are no leather weapons... Hand-to-hand (or claw-, fang-, tooth-, etc) damage is outside this system; nothing, not even daedra lords, are immune to hand-to-hand. As far as I know, all Elder Scrolls games follow that rule. This is probably because
* Dungeons can have disconnected pieces that monsters can spawn into. This is kind of annoying.