A veterinarian friend of mine told me that they all
have to take a course or two in exotics, but it's like any other kind of medicine with specialties requiring additional courses. IIRC, it's like a semester introductory course that's required of everyone.
For example, they all know that the dosage of antibiotics for reptiles is different than cats, but a reptile vet wouldn't have to look up the dosage.
This guy was actually a large animal vet that was in the play we were rehearsing at the time. The back of his office looked like the stockyards with loading chutes and such. However, when a friend of mine had burmese with URI, he said he'd be happy to help and that he knew just the guy to call for a consultation. A buddy of his from school was a reptile breeder and specialist.
It's entirely possible that one of us would know more about some details like morphs and incubation periods of chameleons than even a reptile specialist vet, but that doesn't mean the vet doesn't know what he or she is doing. We study them as a hobby and a passion and tend to focus pretty narrowly on them.
A veterinarian has to know
virtually everything about virtually every animal, but they will either know or have access to more detailed information than an average hobbyist can handle. Some of them won't touch reptiles with a ten foot pole.
Until you know how to draw blood and analyze it, your vet still knows more than you.