Just because your company fails during a recession doesn't make you a bad CEO. It's a stupid litmus test that will get rid of more good CEO's than it gets rid of bad. The stockholders can decide whether or not he's good for the company, and they have more knowledge of it than your blanket firing.
You have a point with respect to Mulally and Nardelli but not for Wagoner. Mulally is relatively new to Ford having become CEO in late 2006. Nardelli became CEO for Chrysler in late 2007. Wagoner, on the other hand, has been at GM for years and years and has presided over its failures. He should be toast.