In much the same way that great revolutionaries seldom make great post-revolution leaders, CEO's are usually incapable of leading a company through more than one set of issues. Great turnaround artists don't work well for maintaining steady, long-term growth. The same goes for great acquistionaries, great sales-increasers, etc. The most recent example of that is Ellen Kullman, whom PlasticsNews is reporting to be leaving the CEO position of DuPont, having spent much of the year fighting of a stupid proxy fight, (probably the stupidest one I've ever seen). While she won the battle quite handily, she doesn't seem able to handle the new challenge.
Earnings for the chemical giant have been lowered for the coming year in large part due to the stronger dollar. This is an issue that CEO's from all international companies have to deal with. Those with a financial background can better handle these types of issues. Being an engineer by training, this is something that is probably out of her league (heaven knows I would be just as unqualified.) Whether the board asked her to step down or she initiated it is unclear and may never truthfully be known. But we can be certain of this: plenty of ink will be wasted on contradictory articles supported by anonymous sources as each side attempts to spin, counterspin and outspin the other. (Just don't expect me to cover it.)