Two points:

1) Ann Coulter did not expose the story that John Edwards had an affair, she just mentioned that the ENQUIRER reported it.

and

2) the liberal media seems to be bending over backwards not to report this story. As this blog points out, if it were a Republican accused of the same thing, it would lead the news every night for weeks. But the Washington Post, New York Times and other liberal sources are deflecting this story as much as possible.