transgender vs drag, tragedy vs. comedy, actors playing across gender

The question posed in the thread "Women playing men: a short list," is how many films entail women playing men. This raised some interesting points about the difference between the relatively rare films entailing actors playing across gender (e.g., Linda Hunt portraying a man in The Year of Living Dangerously) versus actors portraying individuals engaging in gender expression different from that stereotypically expected of their biological gender. The latter could range anywhere from Tony Curtis' and Jack Lemmon's characters in "Some Like it Hot" to Ed Woods' wigs and angora sweaters.

Oh, and there's Monty Python, where almost all female characters are portrayed by men, which the British audiences apparently thought was hysterical.

It seems to me that most often when a male character is portrayed as dressing in drag or acting in a way that's regarded as stereotypically female, it's treated as comedy. There are exceptions, of course, e.g., "Crying Game". When a female character character engages in stereotypically male gender expression (what some might refer to as "trying to pass as a man"), it's often in the context of tragedy, an exception being something like an "I Love Lucy" episode.

Maybe I'm mistaken. I'm interested in hearing what other people think about this and their reasoning.