And so the 40 and 45 haven't benefited from the latest improvements in ammo also?
Sure they have, but the 9mm has really benefited the most from modern ammunition designs and improvements. The .40 and .45 have the benefit of being a larger heavier round than the 9mm. In the past plain old 9mm FMJ was always looked at as a marginal performer. Within the past 10-20 years or so hollow point designs have really become that much better and more reliable making the 9mm shine with a good hollow point. No one is arguing that the 9mm out performs the .40 or .45 ballistic wise, but it is a pretty marginal difference where other factors come into play. Like recoil, capacity, easy of followup shots, price of ammo, and so on... Bottom line is most people can put more rounds down range, faster, and with tighter groups with a 9mm than a .40.