Rigging a building for implosion is a very time consuming and dirty job. It can take upwards of a month or more to get a building completly ready to be safely demolished. It involves drilling into support beams and placing shaped charges. Cosidering the building was in use well before 9/11, it would be much harder.
OK, so let's consider the controlled demolition. How did the team get shaped charges into the building? How could they drill into support beams that were buried behind walls without leavinga huge mess? How could they cover such a large hole in the wall so no one would be suspicious? How could they close off sections of the building without alerting someone? How could they activate the explosives is there was no detcord and no electrical connections?
Know why buildings collapse like that? Gravity, maybe? If the supports in the center of the ground floor are weak, they collapse first. Hence, the building falls in on itself. Now if the supports on one side went first, then it would topple over.
As for WTC 1 and 2, the "explosions" you see are windows blowing out as the floors compress the air as they fall. The Twin Towers were not designed to be demolished conventionally, as the "mesh" structure could not support shaped charges.