I can't fathom the idea of a cop not carrying off duty. What happens when you are at the grocery store and you suddenly run into the guy that you arrested a while back who suddenly decides he's going to get some payback from the guy who (from his perspective) ruined his life.
The larger point to the initial post was that if you (anyone...cop, ccw-holder...anyone) can carry a gun, you should be doing it. All the officers in the article were off duty. The bad guys probably didn't know they were cops when they targeted them. It could just as easily have been anyone...so carry your ****ing gun!