Virtually all Americans over the age of 65 are enrolled in Medicare Parts A and B, which provide valuable hospital and medical insurance benefits to retirees. While Medicare does lessen the financial burden of healthcare on senior citizens, it doesn’t pay for everything. Fortunately, a Medicare Supplemental Insurance policy, also known as Medigap, can help. And most retirees who choose to buy a Medigap plan buy the most expensive type of plan available.