I don't have any stats, but the cases of rhabdo I have seen in the hospital have generally been older people who have fallen, been unable to get up and have been on the floor for a long period (sometimes a few days) without moving. Basically, the muscles in areas they have been lying on have not been getting blood flow and so there is muscle tissue damage from the ischemia. I have also seen milder cases in patients who have had multiple seizures. I'm not sure how the incidence of these kinds of cases compares to that of exertional rhabdo as described in the above articles, but in any case it sounds like there's a problem with the way some people are doing Crossfit.