I was given a WARNING CITATION on klamath lake last year for not having one.

If my tube was one of those relics that only had a single chamber, I wouldnt need one. The logic is, if your vessel/craft/whatever, has more than a single chamber it enters a catagory of a huge scope of vessels.
So they dont have to make specific regulations for each specific vessel, the regulation requires to carry pfd's in any multi-chamber vessel.

Obviously, this is Oregon. But if you are at all confused about your regulations, carry a pfd, then your good no matter what.