Azzam was no small player in jihad in Iraq. He was an experienced and ruthless killer, who as a native Iraqi understood the culture and context of Iraq greater than the foreign jihadis in country. His contacts are likely to be top notch. He will need to be replaced, and his replacement will have less influence and experience than his predecessor. Destroying al Qaeda in Iraq is a laborious process, but one that can be accelerated by taking out vital leaders and middle managers.
This says it very accurately - The shooters down wind have been hunting him specifically for some time - This was a big hit -