The Anderson-Jackson article linked by George is a great read. They make several good points but I think this quote captures the essence of the problem:

“the Jack Abramoffs of the world do not “corrupt” government, as we are hearing today. Instead, the wide reach of government makes people like Abramoff inevitable, as they are responding to the actions and potential actions of legislators and bureaucrats to create economic and social opportunities for some people – and to take away those same opportunities for others.”

The real problem is the scope of government. Only legislators that have the power to coerce wealth transfers can be bribed to exercise that power.