Good post, Sunrise. I agree with everything you said. I think that often personality disorders are not covered under insurance because there is not a "favorable modification or management" system for these types of problems. A pill isn't going to help, and mental health is still treated very much under the medical model of insurance. If there is no tried and true plan of management, it simply isn't covered (like TMJ that you mentioned). That's why often our mental health providers may actually put down a different diagnosis, one they know will be covered. They are working around the insurance system.
I'm actually not sure whether my insurance covers personality disorders or not as I've never had a doctor use that diagnosis for insurance purposes. Hmm.. I'll have to look that one up. I'm curious.