It is a mistake to consider al Qaeda to be any sort of "command and control" operation. Rather, think of them as a Venture Capital firm which nurtures jihad cells.
The role of Osama was not to be a commander as much as a trusted conduit between wealthy Middle Eastern money men (see Golden Chain) and the actual jihadis. Al-Qaeda provided funding and training to groups that showed promise of successfully mounting operations.
Osama is very replaceable. The money men just recruit another cutout to stand between them and the jihadis and maintain deniability.
Thanks for fleshing out the specifics. Well put.