All certification course require a medical questionnaire and doctors release when applicable. My concern is the diver who got certified 20 years ago and was healthy. Now, 20 years later may have developed cardiovascular disease, diabetes, asthma... any number of medical conditions that may limit safe diving. The waivers that are signed to dive (not new certification) typically just ask about "fitness to dive" not the medical questions included in the waivers for scuba classes. Without a medical clearance requirement for these individuals, preventable medical emergencies will happen.
Additionally, is the dive shop within it's rights to ask for a medical clearance from a diver who is 400 pounds, sweating profusely and short of breath while in the dive shop? Or do we just ask them to sign that they believe they are fit to dive and if they have a medical emergency while diving, the shop is released of any liability? And, would that waiver from the diver release the shop of liability. Seems to me that a medical questionnaire is a good idea for all divers but it seems that each dive shop has different requirements.