That has to do with the fact that a lot of patient's with psychiatric conditions are entirely manageable at the primary care level. Most Psych isn't schizophrenia or psychosis, the majority of it is moderate depression, anxiety, drug dependence, and moderate personality disorder. It just depends entirely on how comfortable and how knowledgable you are. But I've seen primary care physicians manage alone a very large amount of disorders and handle a variety of medications appropriately.
FM residencies already can get APA accreditations for having a certain amount of psych rotations or training. These guys generally are very comfortable with psych meds. And I think that it's not a bad idea to have psych training integrated in generalist training as again.
As far as atypicals, many are prescribed by PCPs. There isn't that much special about them other than their disasterous side effects and that you probably shouldn't use them unless you need to. That being said Seroquel is handed out like candy. And I'm personally more fond of Welbutrin and buspar augmentation, but if a patient needs it abilify is a good augmenting drug.
As far as Lithium, Clozapine, truly psychotic or suicidal patients, and patients who don't have their depression respond >50% after trying 3 different meds. I refer them to Psych and or inpatient as they need more direct intervention.