You have to know what you can do wrong before you know what you can't do
A surgeon must know how many and which nerves he can cut before someone is paralysed, but he also has to know where the dangerous spots are, where he can't cut without causing a mass bleeder,... And as a general doctor (so before specializing) you have to learn what the symptoms of everything else is, like asfyxia, poison,...
Or at least that's what I'm convinced of
I don't know how the educational program in other countries is. Anyway, I guess that in real life you would have to do some courses to get accreditation as an ME. (this is what I found on the internet: Medical examiners are fully trained medical doctors with a specialty in forensic pathology who are licensed to do examinations on corpses.)