Your explanation while plausible requires the assumption that in order for the terrorism to be successful that the buildings needed to fall. I agree with you. I don't believe that they had figured out how to make the buildings implode. More likely they followed the law of "gross tonnage"--accellerate a big plane loaded with fuel towards the target. If they hit, they could count on Palestinian dancing in the street.
That there was some sophistication is evidenced by turning off the radars, etc, and (possisbly) flying low enough in DC to go off the radars.
The fact that four planes were used is mere audacity. No one could have expected that. By staying as low tech as possible and looking for huge symbols and destruction, they may feel that their terrorism was effective. It is because we have lived in freedom that much of this was possible. We will remain free, but today means the books are being rewritten. We need to recah to our religious roots in order to find the resolve and strength needed in these times.
The turning of of the transponders is a mere flip of a switch. Transponders are almost always located on the center console of all planes and they are a simple knob with a built in stop that you have to lift up and turn to get to the emergency position( which was not done). Kinda like a dimmer switch on your dining room chandelier. To turn one off is as simple as moving it two positions, past standby to off. The plane in D.C. turned off its transponder after departing towards the west and then doubled back to D.C. It was still on the radar screens (just unidentified, since the t-ponder was off) and only dropped below radar coverage a mere seconds before impact. The planes that did go to emergency on the transponder like the Canada plane could either have turned the transponder to emergency or simply dialed in 7600 or 7700 if I remember correctly and hit ident and the radar operators would have known something was wrong as it would have dropped a box around the blip on the radar screen and made it flash. Squawking 76 or 7700 on a transponder with a hijacker in the cockpit is very unlikely, probably just flipped the tponder to emergency. Regardless of what happened with the tponder, it still is a relatively simple thing to learn, to turn it off that is. Sorry for the long ramble