Yep. And it doesn't even need to be something big and bad for an insurer to deny coverage. Even a minor condition is a risk. And insurers want to avoid things which cost them money.
If you want to have insurers cover people with pre-existing conditions without being punitive (and thereby excluding poor folks), you have to do regulatory (damned socialist) things of some sort.
Markets exclude people. They set prices at a point that maximises profit, which isn't the same thing as universal access. The optimal point on a supply-demand curve will exclude a population which cannot afford the service. Medicine isn't like McDonalds. You can't reduce quality to a manageable level without harming the patient.
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