Unfortunately, there is a limited supply of CEO's capable of running companies the size of these...this is simply a supply and demand issue...if one company doesn't compensate, then another will steal them away.
Severance packages are negotiated when they are hired, and when Killinger was hired nobody could foresee this as even a remote possibility. When he was fired the board replaced him with Fishman, who received a $19 million signing bonus again, at that time the company seemed savable. (Fishmans signing bonus is most likely not touchable...whereas Killiingers severance will be frozen by the bankruptcy of WaMu)...
Performance is another issue entirely. Obviously, these individuals didn't perform. Most have bonuses tied to performance. But their signing bonuses and compensation are set when they are hired.
It seems like a lot of money, but it is what the market demands. Because of the current financial crisis, CEO compensation is likely to increase, not decrease. This is because the CEO's that successfully navigate the tough times will be in even greater demand.