There's commentary, and there's reporting. Hannity, Coulter, O'Reilly, Olbermann, Matthews; they are all commentators and should never be confused with reporters. PMSNBC blurred the lines and got caught. When networks have commentators masquerade as reporters, things get ugly.
Dan Rather got caught up in that whole "reporters are now the stars, we're the news" thing that developed in the 80's in the same era as the movies "Network" and "Broadcast News." FTL nails it above.
The interesting part of the Rather story is that he did not screw up on his NEWS show but on the Magazine show which was opinion/commentary. He was essentially trying [poorly] to fill two roles.
I have always contended that as long as the Broadcast Journalists are treated as celebs and act like celebs they tend to lose their credibility. They throw softballs during interviews instead of the hard questions and they cozy up to the power brokers in social settings. VERY convenient for the power brokers as they find it easier to slide things by their friends.
Olbermann and Matthews are in a weird position in that I don't think they have desire to be in the NEWS role, preferring to be in the commentary side of the game where THEIR OPINION is part of the formula. I am sure it is the case for Matthews as one of his producers is in my NYU classes and we have talked.
MSNBC is in the position of trying to find a niche. And the sorting of players is part of that. When Tim Russart died that threw their entire fall plan into disarray. It is going to take much to regain it and they will continue to lose until that happens.
Gregory is a very good choice as a replacement in that he does not care about career as much as he cares about getting the questions answered. That should, in the long run serve the public well.