The problem with this theory is that skyscrapers are not stronger at the bottom than the top- they're *thicker* at the bottom, but then again they've got more weight on them, so they have to be.
So if the top collapses, and it falls and overloads the next bit down by 50%. That in turn falls and overloads the next bit down by 50% (because it picked up the next stories weight as well) and so on. At each and every point the overload percentage is the same, and so the whole thing fails together.
And that's because these buildings are designed to be equally stressed at every point, because that minimises the construction cost.
The kind of failure you saw at 9/11 is exactly what you would expect.