@Al R: 16 of 155 generals in WW II who commanded divisions were relieved of command (two or three we later given other commands) ~ (snippet from Tom Ricks' "Lose a General Win a War" article from 2010 that accompanied the firing of General McChrystal)
Patton relieved one of his division commanders in North Africa, and from my readings of his history, I think three or four in France. (Not sure which book on Patton this comes from, but he had a discussion with one of his corps commanders about "if you don't relieve General X, I'll relieve you.")
@MPN11:
A good half of the Sec Def's job is politics. The other half is making sure the nation can apply military means when and where needed.