I took my car into the shop yesterday for some body work after a minor collision. Because all i had to do was to pay the co-pay, i didn't really shop around for the best deal. I suspect the same mentality applies to most people when it comes health insurance and co-pays. Thus as long as everyone charges a similar amount, they can all over charge without concerns, and the consumer doesn't really care.
A better system might have been instead of a flat co-pay, use a percentage based co-pay, with plans for 5%, 10%, 20% etc co-pays. Thus there would be an incentive for the consumer to price shop. For health care, cost must be itemized and be more transparent. And to assist consumers in choosing the right provider, a rating system for the provider must be available. Any such ratings must consider how sick his/her patient is before care, and how sick they are after care.