Exactly how the plot to blow up ten airliners en route from the United Kingdom to the United States was foiled may not be known for some time. What we do know at this point is that it was not a success in the "war on terrorism." It was, instead, a success of the law enforcement approach to terrorism.
Scotland Yard, based on information provided by British, Pakistani, and (almost certainly) American intelligence agencies, conducted surveillance and local police made arrests at the point at which either the bombings were believed to be imminent or sufficient information had been gathered to be able to arrest and charge all of those involved. Police work and international cooperation were the keys to success, not a war against some suspected state sponsor of terrorism.
It's worth noting that the principals in the plot were apparently all British citizens. (So far, there's no word that the United States is planning to invade the United Kingdom.) Timothy Garton Ash considers Britain's failure to assimilate its Muslim population more effectively in an interesting commentary here. So perhaps, on the basis of what we know about the roots of Muslim rage in Western societies, we should be doing more with the social work approach to terrorism as well.
In time, the so-called "war on terrorism" will be recognized for what it is: a politically useful phrase akin to the "war on drugs."