I believe you are correct. The problem arises when instructors or dive operators think they have the expertise to look at a bunch of Yeses and Noes and make a medical judgement. They are expressly told by PADI NOT to do that; those questions are there to allow the instructor/operator to be able to tell a student they need to see a doctor, and if they have already seen a doctor, the job is done.That clarified an important point for me; when you don't check the 'yes/no' questions, you've already got a physician's statement attesting to your readiness to dive.
Many people who show up at a dive shop or dive boat and fill out the customary paperwork, including liability disclaimer, do not have a medical release from a physician, and I suspect their situation is 'Check 'no' to everything or you don't dive with that operator that day.'
So, either get the letter in advance, or check 'no' to everything, or don't dive.
At least in the U.S./Caribbean diving I've done, that's been my impression of how the system works. Is that impression in error?
Richard.
If someone wants to answer all Noes, so as to avoid the doctor's signature thing, they are not going to go to prison for lying. However, given the fact that you sign the form on the front saying your answers are accurate, you may indeed have a very uncomfortable discussion with your insurer (DAN or whomever) should a medical problem that arises.