Take another look at the footprint and understand that it was only the design and construction of the retaining walls that made the difference, Any flaw would have led to a much bigger mess. The fall of those building had the force of a small earthquake. Fortunately they did not fall at the same time.
As some one who watched the Trade Center go up and worked in and around those buildings for almost twenty years, I don't have to look at the footprint. Between the Trade Center and the Hudson River are a couple of hundred yards of earth upon which is built the World Financial Center. As for your comment that Lower Manhattan would have been washed away, your ignorance of the geology of the area is astounding.