Obesity is not the disqualifying factor. It's usually the problems that come with it that cause people to fail. Hypertension, Diabetis and Sleep Apnea are the most common with it. Those that fail would be hard to track down, especially with witchdoctor types out there willing to fill one out for the right amount of money.
UMMMM...if you fail the medical....you aren't a driver till you can figure out how to pass. Think about it!