Actually there were four towers originally, with the mast being a middle finger to China. That's why they funded terrorists to blow up the towers. The attack was only partially successful, knocking down just two towers. George Bush couldn't bear to see only half of his towers remaining, which is why he sent the planes in to finish the job.
There's a misconception about the insurance of the towers, some people think that only one tower was insured, in reality both towers were, but on the same policy. After the attacks, the owners of the towers tried to claim damage on both towers as if both were destroyed independently. The judge sided with the insurance companies, that it was only one attack on both towers, so it counts as only one event to be claim.
That seems like it shouldn't matter... Either two half size payouts or one full payout is what it seems like it should be. I'm sure there are some shenanigans that make it not that simple when it really should be.