Which states that a dive medical is required for courses, not for normal recreational dives. I have never been asked for a medical certification on any dive that i've done here. On the dayboats that I have worked on we check C-cards - and will turn you away if you can't produce one- but we never ask for proof of a dive medical.
On the Liveaboards that i've done, I have had to fill in a self certification form as part of the liability release but have never had to provide an form of official certification.
The above notwithstanding, getting a check out from a medical professional on an annual or bi-annual basis is not a bad idea. After all, you get your kit serviced regularly, why not the really important bit that the kit is designed to preserve ?