I was talking to a Chinese friend the other day about corruption in China and the US. He asked what I thought lead to the reduction of corruption in the US. I suggested that it wasn't the government, but the relatively free media in the US that was probably most responsible for the decrease of corruption over time. I believe that the media was/is often used by competing interests as a way to keep the other from gaining a non-legal advantage. Of course, the courts often perform this service, but the 4th estate can challenge corruption in the legal system itself.
As dirty laundry can be effectively used by any party over another, everyone feels a pressure to keep their laundry clean.