Let's put things in context here. I'm just a CPR certified trainer, no medical background properly speaking, although I do have an M.Sc in kinesiology. I'm 255 lbs, and chances are I'll be nervous as hell in a situation where people are relying on me to save their lives.
I'm not saying breaking a rib/s, snapping off the rib from its cartilage attachement, etc, happens every time, but it does happen pretty often, enough to make one consider giving CPR if that means being sued later.
I'm talking from a Canucks/tourist's perspective here, as I visit the U.S a couple of times a year, in different states. Kind of a bother to get that info every time you go to a different state, huh?