The single biggest hurdle for women in sports is the segregation in adolescence. Once you stop competing against the highest tier of peers it's hard to keep pace.
Edit - to add to the above. The best example of this is American Men's Soccer. Are American men physically incapable of being competitive at the highest stage? Something to do with anatomy? Or is it that American youth leagues don't have anywhere near the skill and depth of competition of those found in other countries and subsequently that talent isn't developed at a high enough level?
A big hurdle is, for sure, the quality of competition and leagues the players are playing. Also, of course, what is a promising young athlete choosing for her/his sport, because someone like Jackie Joyner-Kersee or Bo Jackson could've been elite in many different sports.
But in this "men vs. woman" debate, the biggest hurdle, by far, is the physical one.
This is not hockey (even though Hextall is mentioned, as the goalie of the US team was phenomenal):
Also, even if you are not an athlete, just talk with your athlete friends (female or male) about the physical differences/performance.