That may be true when it pertains to gynecological exams, but I'm male and it's not true for my exams. I've had female doctors that have a female chaperone. It's really a double standard -- but it is what it is.
Just to be specific about your exams with a chaperone present: what exactly would be so potentially distressing that a doctor would feel it necessary to protect herself from false accusations on your part? What part of the exams you've had could possibly be construed as evolving into something that is perceived as being inappropriate?
Now don't understand me wrong. It's nice to have 2 females present during an exam, nice in a medfet way that is. And if it's medically or technically necessary, then it's nothing to give a second thought about. No one should be a prude when it comes to health and medicine.
But medical necessity aside, what part of an exam could be thought of as potentially inappropriate that would need a corroborating witness? And if doctors start to think that all their patients are potential slanderers and false accusers, well, why should they even take any of their medical complaints seriously then? By reasoning that too could just be a fantasy on the patient's part ... how can a patient trust a doctor who doesn't trust their patients?
And the next logical step in this process of distrust will be to consider a witness unreliable - after all it would be the typical he said/she said, word against word. So what is next? Video recordings of exam sessions to have proof of what happened?
This seems to me to be an archetypal slippery slope. Once a (medical) society starts on this path of distrust, there is no way to predict how it will end up.