Maybe someone with more knowledge of history can help me, but my impression is that women tend to rise to higher ranks in parliamentary governments than in governments that split executive and legislative power between two branches (like the US does). I can think of many female prime ministers, but I can only think of a few female presidents (any in a government with strong presidential powers?).
Similarly, women have thrived in America's Congress but none have yet made it to the presidency. Hillary Clinton is the closest yet, but I personally don't think she has a chance at winning (unless she can run against Huckabee perhaps).
On the other hand, America has plenty of female governors who wield a reasonable amount of power -- but don't have any responsibility for foreign relations.
Is my impression wrong, or if it's true is there some reason for it? The only thing I can think of is that executive power parliamentary systems is wielded by members who gradually rise through the ranks through seniority, whereas in presidential elections seniority can actually work against you (voters always wanting "change").