"Al-Qaeda is no longer the hierarchical organisation that it was before 9/11. Three-quarters of its senior leaders have been killed or captured," the official said.
"What you have had since 9/11 is growth in the Islamic jihadist movement around the world among groups and individuals who may be associated with al-Qaeda, and may have financial and operation links with al-Qaeda, but have no command and control relationship with it," he added.
With the start of the "war on terror" Bush officials and self-described counterterrorism experts tried to picture Al-Qa3da as an professional army, with bin Laden as its commander in chief. The discourse of the US intelligence community was to change later, to allow room for recognizing that the Al-Qa3da was more of a network, or more accurately an "idea," than it being an organization. Dissolving bin Laden's office marks the official end of this stupid view.
A good book I recommend on Al-Qa3da is Jason Burke's "Al-Qaeda: Casting a Shadow of Terror."
Here's also another article on the decentralization of Al-Qa3da: Crusaders and Allah's Soldiers