Democracy, Form Not Substance

In his latest, Fareed Zakaria shows how the debate has changed from whether Democracy is compatible with Islam to whether Democracy, broadly put, can combat "old-world hatreds", as I call 'em. He also throws in corruption.

I suspect this could and will occupy political science PhDs and sociologist for a long while.

How does it come to pass that democratically elected governments do not trend away from corruption of the public interest?

How does it come to pass that a populace fails to elect a government that is responsible to the whole people, not just a portion of it?