This is a statement repeated quite a lot. I have never seen data backing it up other than wild-assed guesses.

The leadership and organizations that are being destroyed are not easily replaced. There are reasons leaders of al Qaeda and other groups become leaders, and just plugging another warm body in isn't as easy as you think. The captured writings of the terrorists talk about the damage being done to them.

You do realize that the entire thesis that "we should have gotten bin Laden if we really wanted to do some good" is BASED on the idea that terrorist leaders are important?

That doesn't mean we've got an easy victory going. Although al Qaeda is on the ropes in places like Anbar, they are still strong in Diyala. Iran and Syria are backing the terrorists with money, weapons, and training. Al Qaeda is finding a comfortable haven in Pakistan, a nation we aren't going to be invading any time soon. And of course, al Qaeda isn't the only problem in Iraq.