Much like how blushing can unconsciously reveal sincerity or embarrassment, tears are an uncontrollable sign of submission and/or emotion. Thus women are shown as non-threatening and more easily understood.
There's a question in evolutionary biology of why women blush and cry more than men (not to mention why such reactions exist in the first place). One theory is that these involuntary reactions are useful as a visual display of emotion to men who might otherwise miss cues that are present in other forms of communication.
