The reason al Qaeda hasn't been as dangerous or prominent since 9/11 could be because:
a) they never really were that dangerous to begin with, and 9/11 was pretty much an "all-or-nothing" attack.
b) they're laying low now because they know someone's going to have a bomb sight on their rears the moment they show their faces.
c) we've managed to kill, capture, or demoralize a majority of their members.
