Outrageous Medical Costs

I was reading this article on JS Online, and started wondering "why?"

Cardiology: Intravascular stent placement Milwaukee: $2,176 Detroit: $510 Cincinnati: $551 Orthopedics: Arthroscopic knee surgery Milwaukee: $962 St. Louis: $629 Cleveland: $653 Radiology: MRI Milwaukee: $945 Cleveland: $531 Kansas City: $531 Gastroenterology: Colonoscopy Milwaukee: $640 St. Louis: $389 Cincinnati: $392

I don't know much about how they price medical care, I just know it's a lot higher than it use to be, no matter where you live. I'm praying I never have to go to Milwaukee for any kind of treatment. Maybe I missed it, but I didn't see any explanation other than the lack of competition in Milwaukee. I wonder if they charge more because their malpractice insurance is a lot higher? The article didn't mention it, but that seems to be a problem everywhere. Just curious.