Enlightened newspaper editors and owners have come to understand that when they endorse a political candidate their news coverage becomes suspect in the eyes of readers, even though most reporters are basically fair and accurate.I'll take it a step further and ask why newspapers would have any editorial opinions--unsigned pieces attributable to the editorial board of the paper--whatsoever. Once newspapers have presented the facts that a reader would use to make up his or her own mind, of what incremental value is it for the newspaper itself to draw a conclusion as if it represents the views of the organization? Having a strong ideology in any part of a news organization calls into question--in appearance if not in fact--the lack of that ideology in other parts of the organization. One would think that any threat to the integrity of the news coverage would be avoided at all costs (financial and otherwise).
There is a popular demand for editorial and opinion writing, and there is still a role that newspapers can play in this regard. They can assemble a team of columnists that provide a wide-ranging but balanced set of opinions--opinions that are directly attributable to the author and not the paper as a whole. I think the Washington Post does this better than any other major paper, but I don't think they do a substantially better job than my usual trifecta of Andrew Sullivan, Powerline, and Brad DeLong. They may still command a bigger readership than blogs, and so could use access to that readership to enforce higher quality from their columnists. I don't think that happens nearly enough.
I also think that the mainstream media will improve (eventually) due to the competitive pressure from blogs, in two areas. First, the MSM will become better about linking directly to sources to provide factual support for its arguments. Second, the MSM will become better about correcting factual errors as soon as they are pointed out and in a more forthright manner. I guess we'll have to hope that these two changes happen sooner rather than later.