.40 has just as much stopping power as a .45 and the mag holds more rounds. most PD's are going with .40 due to the fact that it is better than 9mm and .45. NYPD went to .40 after alot of research and testing and they have 45,000+ officers, they carry Glocks. the US government is also going to Glock, you may have seen there guns, green frame and black slide.
ball rounds don't cause as much damage as a hollow point. the idea behind a controled expancion round is to shut the brain down with shock from the amout of damage. the brain can handle ball rounds better because the will just go in one side and out the other with out much tissue damage.
i can back up everything i said if there is any question about what i said.