A new study found that editorial pages were more likely to give space to opposing viewpoints in letters to the editor and to op-ed articles. Published in American Politics Research. the Yale University study, which I read about in the Boston Globe, sought to test the bias of newspapers editorial pages.
The results: "Newspapers were more likely to express interest in a letter if it went against the position expressed by their editorial page, which explains the greater interest in pro-McCain letters, since Obama was endorsed by more of the newspapers. This suggests that editorial page editors are driven more by a desire for balanced and contrarian reporting than sheer bias."
So it seems that organizations are more likely to get coverage if they write in with a letter that opposes an editorial than if they write in to support an editorial.