Forget too big to fail. In the eyes of federal regulators, many Wall Street firms are too big to punish.

During the past three years, some of the nation's largest financial firms have been accused by the government of cheating or misleading clients and ripping off tens of thousands of consumers of their investments.

Despite these findings, these financial giants got, sometimes repeatedly, special exemptions from the Securities and Exchange Commission that have saved them from a regulatory death penalty that could have decimated their lucrative mutual fund businesses.