The field of Psychiatry is the only topic mentioned in the help that is not, itself, a science.
It's like a physics Q&A site where they would include engineering or a biology Q&A site where they include medicine. While there is, of course, some overlap, there are lots of engineering questions that have nothing to do with physics and medical questions that have nothing to do with biology (or you could throw chemistry and medicine together).
Including what we have included other than Psychiatry includes all of the relevant bits of Psychiatry as well.
As it currently stands these are all acceptable questions.
Is Freud's theory of the oedipal complex useful in diagnosing schizophrenia? That's a potentially scientific question but the entire foundation has been soundly tossed by all modern science so anything starting with Freud isn't really within the scope of science. It's like asking an astronomer in what direction Venus moves around the earth. However, under Psychiatry psychoanalysis is still practiced. Furthermore, psychiatry includes lots of relatively archaic, but still practiced variations so question on Jungian therapy, Gestalt, etc. would be included. I'm not saying all related questions should be excluded but a scientific answer directly related to their current practice isn't really possible; whereas scientific answers about their efficacy, effectiveness, and empirical support can be answered. But those can fall under psychology.
How should I select a Psychiatrist? Again, this is currently an acceptable question because we're including psychiatry and any remotely related professional questions should be accepted.
These are just two questions that I think really don't fall under Cognitive Sciences. I can't think of any questions that we'd lose if we dropped Psychiatry that we would want to keep. Can anyone else?