"NEWSWEEK asked Wealth-X, an intelligence and research firm, to compile a list of the 50 highest-earning political figures of 2010.
Included in the rankings are politicians, ex-politicians, media personalities, and political consultants.
NEWSWEEK's Power 50: The List - Newsweek
I'm guessing the book writers and those not currently in office make extra (above and beyond their salary) for selling themselves for speech giving. Example, President Obama may be richer in 2013 than he is in 2010 because he'll be able to sell his services as a speech giver that he can't do now while in office. I suspect he'll move up on the list after he's out of office like Bill Clinton.