Hospitals charging different prices for same treatment

Getting back to prices of healthcare, it seems that some hospitals are ripping patients off, charging more for services even than hospitals in the same city.  This is according to an AP article titled "High hospital bills go public."

The article ponders some interesting questions:

Why does a joint replacement cost 40 times as much at one hospital as at another across the country? It's a mystery, federal health officials say... The average charges for joint replacement range from about $5,300 at an Ada, Okla., hospital to $223,000 in Monterey Park, Calif., the Department of Health  and Human Services said.  That doesn't include doctor's fees... Hospitals within the same city also vary greatly.  At Beth Israel Medical Center in New York, the average charge to treat a blood clot in a lung is $51,580.  Down the street at NYU Hospitals Center, the charge for the same care would be $29,869. 

Interesting.  I wonder what the different costs for breathing treatments are?