I think that there's an overemphasis on the form itself which clouds the separate issue of whether you are in fact fit to dive. Like a prior poster, I'd prefer a form that listed medical conditions that potentially contra-indicated diving. You'd initial each to show that you've read it, and sign a general release at the bottom saying that you have none of the above or provide a doctors letter that stated that while you had a condition, it was not, in his opinion, a problem.
As it is, the form does a poor job, and does create serious privacy issues. For purposes of debate let's divide the purpose into 3 issues and consider each.
1- actually keeping folks with medical problems from diving. Here it does a so-so job, if someone knows he has a condition, but isn't aware of how diving would affect it (or vice versa) it'll flag the problem, and send him for a professional opinion. Two problems. First, large numbers of people have undiagnosed conditions and won't find out until a crisis. Second, the form is generic, and doesn't separate conditions with specific contra-indications to diving from others, and there is no guidance given to General Practicioners about medical issues unique to diving. For example; do all MD's know the physiological effects of submersion in cold water, or how it might impact a mild heart condition differently than excercise in general. The end result is that even the doctor's opinion may be uninformed and inadequate.
2- Safeguarding the physical safety of DM/instructors, who face the consequences of dealing with problems under water. There's a catch 22 here, if the forms are simply tucked away unread to protect privacy, or the people involved remove themselves from the equasion by dealing with this digitally - doctors letter = OK, no letter = NG, they draw no benefit from the form itself. If they inject themselves into reviewing the decision process, they assume a degree of legal liability.
3- legally protecting the vendors. This is what the form does best, It documents imformed consent, whereby the diver signs a document that he has no relevant medical problem, or a doctor signs the same. The dive operators, associations and employees are removed from the decision. The diver is forewarned of possible problems and assumes the risk. This purpose is served whether the signer lies or not.
So coming full circle, if you are in fact fit to dive, the form is nothing more than a legal release protecting the operators and the details are imaterial. If you're in fact not fit, you shouldn't be diving, form or no form.
just my 2 cents worth, maybe worth even less than that.