Calltips will be rewritten for 3.5, maybe 3.4 in #19903, to use inspect.signature. Once that is done, I would like to revisit this issue, as I agree that it would be useful, and it should be fairly easy. I though of being able to rightclick on the calltip box to ask for more but a key would be fine to start. The current code uses .__doc__ but only after checking that it exists.
    if isinstance(ob_call, types.MethodType):
        doc = ob_call.__doc__
    else:
        doc = getattr(ob, "__doc__", "")
    if doc:
I would not start this until the new code is in place.