You just contradicted yourself by saying that men an women have physical differences.
Regarding your last sentence, have you ever heard about the Nordic gender equality paradox? There are two reasons why women are not working in such fields. The first one is economical: as you said, women are indeed physically weaker than men, meaning less productive for heavy duties, so no one would be willing to lose money by hiring them rather than hiring a men; And the 2nd one is... they simply do not want to pursue such careers!! Go to youtube and search for "the gender equality paradox" and have fun. Women (and men) behaviour is result of thousands and thousands years of evolution on the simplest way possible. Civilization is something rather new to our species. Prior to that all our premises were based on a simple rule: the survival of the fittest. This same rule molded our, men and women, brain/body/mind/behaviour differently from each other.