Why did Keith Olbermann have to sign off?

Keith Olbermann signs off. http://on.msnbc.com/gXQFSN

I found that some people classified him in the same group that Glenn Beck belongs to. But he not only takes a different position on several matters from Glenn Beck, his style of speech is also more restrained and logical than his "counterpart." I wonder if my impression is not shared by most of the people in the USA.

"One week, the Right's theme is 'Obamacare’s death panels'; another week, it’s the 'Ground Zero Mosque'." What the Hell Happened to Keith Olbermann?: MSNBC's parent company, General Electric, never seemed comfortable with some of Olbermann's material. http://bit.ly/eHycQy

“Unlike News Corp. chairman Rupert Murdoch, who stands solidly behind the right-wing propaganda on Fox News, the corporate owners of MSNBC have no similar commitment to the work of Olbermann, Rachel Maddow and Ed Schultz." Robert Parry http://bit.ly/eHycQy