>> My understanding is that if a little guy evades taxes, but then cooperates with the IRS when caught, and agrees to pay all taxes and interest and penalties, then they generally don't get thrown in jail

Where in the world did you get this idea? If you don't pay fully or on time, but don't lie, they just make you pay, because that's not "evasion."

Elaborate premeditated lying using fake books or shell corporations to deliberately hide assets is a serious crime, which the rest of us can't get out of with our armies of lawyers and well placed phone calls to politicians.