Why General Petraeus?

Hello and welcome to all of the admirers of this blog....
The U.S. Senate confirmed General David Petraeus as director of the Central Intelligence Agency on Thursday.The senate voted 94-0 in favor of the architect of American counterinsurgency strategies in Iraq and Afghanistan.
Petraeus replaces Leon Panetta, who is the new secretary of defense. Panetta replaced Robert Gates, who retired.
Well this is the news which confound me and also many other people of the world. Petraeus headed the U.S. and NATO forces in Afghanistan since 2010. He is leaving the post as the U.S. starts reduction of its troops in Afghanistan by 10,000 soldiers this year and 23,000 next year.
The thing which also induced me to write on the topic, is that Robert gates was the first person who criticized America after the Abbot abad operation. He was the secretary of defense at that time and he opposed the American violation in open words and not care for his designation. HE SAID
"US HUMILIATED PAK BY CARRYING OUT ABBOTABAD OPERATION"
So many of the Americans officials favors and some opposed his brave statement.
On the other hand he is the same general petraeus who was trying to negotiate with the afghan Taliban on the behalf of Super power America. He is the same general whose leadership gave America a chance to think of removing Taliban from terrorist list.
An other side of the picture is, the relations between the CIA and Pakistani ISI were deteriorated after the Abbot abad operation. and are not up to the level as were in the past. So this may be a confidence building measure from US.
But why Robert gates got retirement at this crucial time?
And why general petraeus?