The takeaway is, all shots to the CNS for the win! ;-) He switched because he had something like 14 rounds in the perp, several of them in areas thought to be sure stoppers, and he only had 4 rounds left when it was all done. He simply didn't want to come up short on ammo again.
Personly, this brings the Mozambique drill to mind. If COM shots aren't doing it, aim for the brain! I carry 9mm because it is SUPER common and ammo can be had EVERYWHERE, followup shots are pretty easy, capacity is good in most modern guns, and VERY effective rounds are readily available for carry use.
My personal sidearm is the Glock 19. One in the pipe and 14 in the mag with a second mag at the ready. If I can't do the job with 29 rounds, then I have gotten myself in some DEEP Kimchi!