Fred Wilson with some observations on CEO changes after the Google and Apple transitions this week:

Too much change at the top can be bad for a company. A CEO for life can be bad too. Something in the middle is probably better. And if you are going to have change, evolutionary change where the company has time to get to know the new leader before he or she is elevated is ideal.
It makes sense.

Look at someone like Carly Fiorina, who came into HP with guns blazing about how the company would change. She was successful in her first year with short-term change, but in the long run, well, we all know how it ended.

It takes time for a new CEO to get to know the role and vice versa, for the company to get used to operating with them at the helm. The relationships of trust have to be developed. This is also why the best CEOs are the ones that are promoted from within.

Change can be a good thing, as long as you promote the right people and continue to keep the right people around them.