If we were talking about a fantasy movie with magic and such, then sure, whether it's a man or a woman shooting fire out of their eyes is pretty much a moot point. Equally impossible in either case. When it comes to action movies, though, that's not the case. The odds of 6'4, 275lb Dwayne "The Rock" Johnson winning a fight against four or five guys are exponentially higher than those of 5'3, 105lb Lucy Liu.

In the case of the male, victory requires (admittedly extreme) luck. In the case of the woman, victory requires breaking the laws of physics. All I have to believe for Dwayne to win is that his opponents are morons who attack one at a time, who always make a small sound before attacking from behind, etc. But for Lucy to win, I have to believe that a 105lb woman can punch a 200lb man into unconsciousness without breaking her wrist.

It's basically the difference between watching a football player throw a 50 yard pass through a small tire 50 times in a row, and watching him do the same thing with an anvil. I know the former feat is ridiculously unlikely, and squarely in the realm of fantasy. However, I know that the latter is impossible.