A legal issue that the RSTC medical form may be dealing with is the idea of informed consent. I investigated the case of a dive fatality in which the expert witness hired by the plaintiff, a person who serves as an expert witness in a lot of scuba-related lawsuits, argued that the liability waiver the deceased had signed had no value. He said people routinely sign them without reading them or (if they do) understanding them. Unless the instructor could prove that he had gone over each item, explained it in detail, etc., it was not valid. IN fact, he said it would not be valid of the deceased had not consulted with an attorney before signing it.
As an instructor, I have read a number of warnings stating that I should go over every clause in a liability waiver before the student signs.
I suspect that the same could be argued in the case of someone who signs a simple statement saying they have no medical issues; how do you know you have no medical issues if you do not know what those issues are?