It looks like there might be something to my initial hunch that GM CEO Fritz Henderson was ousted because the company is now stable enough to make a change it's board has wanted to make for a while. Today's Times story explores that angle a bit, in any case:

According to a person with direct knowledge of the board’s deliberations, there was no final straw that led to Mr. Henderson’s forced resignation. Rather, G.M.’s directors began discussing weeks ago that the company needed to seek an outsider to lead the company.

“Fritz was just not enough of a change agent,” that person said. “The board wants a world-class C.E.O. and now they have enough breathing room to find one.” ...

The more you learn about the GM situation, the more apparent it is that Henderson never had a real chance to lead the company. In fact, the auto task force wanted to appoint him interim CEO after it ousted his predecessor, Rick Wagoner, in March. But Henderson persuaded them it would be almost impossible for him to make changes at the company if the government labeled him a temporary caretaker. Still, just because he ended up getting the title he wanted doesn't mean the board (and the government) ever really saw him as anything other than a transitional figure.