Health Insurance Regulation

A question I've wondered about: how much of our high health care costs in America are due to government-mandated insurance features?

If the government let insurance companies choose whatever features they wanted to include or exclude, we would expect the efficient level of health care. Heart transplants, for example, might not be covered by most employers. Autism services almost certainly would not, since the moral hazard is too great.

Anyway: how onerous is regulation? Do we have a reason right there why Americans buy more health care than Europeans-- it's because it's a government mandate? Here is a good 2004 report listing mandatory state coverage, from an underwriters' trade association that is critical of it.