Utter nonsense! JUST LOOK AT THE WAY THE BUILDINGS COLLAPSED. Really; Take 15 seconds and look at the way the buildings collapsed. Damn it, man! Had the bottom portion of the core been weakened by explosions designed to take down the building, tens of thousands of tons of top floors collapsing on themselves would have caused the ENTIRE building to collapse simultaneously, or you would have at least seen the bottom of the building shift under the weight of the collapsing floors.
Or are you saying that some demolition crew was SO GOOD that they calculated the exact number of support members to cut, the exact number to remove and the exact amount of explosive force necessary to simply weaken the bottom of the building just enough so that ONLY when REST OF THE ENTIRE FRIGGIN' BUILDING finally landed on the bottom floors, the bottom floors actually collapsed? Is that what you're saying? If so, what in hell would that have accomplished? Gravity is a whole lot cheaper.