The article only touches on lobbying, but that's the key mechanism by which wealthier people gain an unfair influence on government. As campaigns have gotten more expensive, the system selects for those politicians that raise enormous amounts of money – people who cater to the lobbyists. Lawrence Lessig did a phenomenal job breaking down the campaign finance / lobbying problem in his book Republic, Lost: http://www.amazon.com/Republic-Lost-Money-Corrupts-Congress/...

I also found the Lawrence Lessig / Jack Abramoff interview very illuminating in understanding the corrupting influence of money on government. It's long but worth watching: http://www.youtube.com/watch?v=pkvIS5pZ0eI