For most working Americans, paying their share of the taxes that fund Medicare is an unavoidable fact of life. It's so automatic for many workers that they may not even realize it takes a bite out of every paycheck. In theory, everyone is required to contribute to the country's health insurance program for seniors, no matter how poor or rich, from cashiers to CEOs. Not on Wall Street. There, some of the most powerful people in finance found a way to opt out.