The Secret Service prepares plans for a variety of attacks that they catch wind of, and they had been informed, as had Bush, that terrorists were planning to use airliners as bombs. This is what is in one of the links you ignored.
So in your world, the second the planes hit the WTC, everyone should run in a circle and say, "Oh shit, we're fucked, what the hell, what's going on here, oh no!" In reality, their plans were predicated on the fact that they were aware that exactly this type of attack was being planned, but they didn't have enough information on the when to prevent it. So, it starts happening, and they are unsurprised because they had some info, not because they plotted it.