My friend was talking to an architect who worked in NYC and he said after the first twin tower bombing all skyscrapers had to be wired for demolition. The first attack occurred in the 90's. The guys rented a U Haul, packed it with explosives, and parked it in a corner of the tower. The plan was to topple the tower domino style which would have been very destructive, but the tower did not fall. Realizing just how bad it would be if a skyscraper were toppled, the city secretly ordered all skyscrapers be wired to go straight down in case of attack. So this to me seems plausible, and would make a nice explanation of when exactly the twin towers were wired to be brought down, as well as why tower 7 was wired to go too.