Police departments across the U.S. are facing budget cuts as taxpayer revenues continue to fall. This results in reduced dollars for training and supplies and reduced numbers of officers. A police officer with limited pistol training is going to score better with a 9mm than the 40S&W because of reduced recoil. As the story said, the crux of the matter is falling qualification scores for police officers, and that's why the change.
Let's face it, how many times a year does the average U.S. police officer have to shoot someone? The real question is more like how many times a decade does the average U.S. police officer how to shoot someone, because the short answer is, they don't. Their job isn't shooting people, it's enforcing laws. They need to meet the minimum requirement for marksmanship and that's it, from a realistic, practical perspective. And changing to 9mm will make that a little easier in times that are tight for money.