Rustbucket, you miss the point beautifully. The whole point of the WTC horror was that it was committed by pax, with minimal weaponry, but a willingness to die. I very much doubt that UK security would have caught them either. They could just as easily have used "legal" knives- the thing that made them dangerous was their fanaticism, and that is not easily detectable at an airport.
All the measures we are seeing now are very much a matter of bolting the door long, long after the horse has departed the scene. Mostly it is about restoring passenger confidence (as good a reason as any, I guess). The only real defence is preventing them getting into the flight deck, and I very much doubt that any of these guys would have appeared overly suspicious at check-in or security.
I am all for security, as long as it is intelligent and sensible. Ask El Al about cockpit security if you want an example.
Finally, I really feel for the poor security staff around the UK, having to implement DETR procedures and getting abuse from everyone... let's try and be nice to them.