This case is a perfect example of how emotion gets in the way of logic and why we find it so hard to solve the health care problem. Every health insurance plan and every health benefit plan through an employer has a subrogation clause requiring that medical bills which are paid by the plan are to be reimbursed if a third party is responsible for or actually pays the bills. This is to keep the cost of the plan low for all participants and to avoid duplicate payments. So in effect since these were medical bills were paid by the Wal-Mart plan they are reflected in the premiums that its employees pay for coverage.
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QuinnsCommentary 
This is not unlike when you hear about a fund raiser for people with high medical bills and nobody asks if they have coverage or not, it's just assume they need the money. A few years back my sister had a child with hundreds of thousands in medical bills. The town where she lived organized fundraisers and received $50,000, but my sister could not take the, her insurance covered all the costs.