MikeFerrara once bubbled...
First off I am not at all against some type of periodic testing/recertification for instructors. On the contrary I believe we need it. The problem there is do we currently have a valid test? If we did maybe we wouldn't be having this conversation.
Certification at the diver level though is not a license. The effects of a divers actions on others is very limited (like any other activity). That isn't true for doctors, lawyers or commercial pilots.
To answer your question, for some ratings I am required to teach a minimum number of classes per year or go through a recertification process. Hey that's like what pilots do, they have to have so many hours in certain environments or do a check ride with an instructor to become current. For others I am only required to pay the anual membership fee and show proof of insurance. Of course the above assumes there have bee no QA actions and you are in good standing with the agency.