Nevermind that without the 408-foot spire, One WTC is shorter than Chicago's skyscraper (which still leads North American buildings in having the highest occupied floor), there are reasons beyond rankings that make the Sears/Willis the tallest tower in our hearts.
A true marvel of skyscraper engineering, the building is designed to sway up to three feet in high winds.
It Expands Our Horizons
According to the Willis Tower's SkyDeck facts, visibility on a clear day is approximately 40-50 miles (65 - 80 kilometers) meaning viewers can see four states from the tower: Illinois, Indiana, Wisconsin and Michigan.
It Inspires Crazy Stunts
Climber Dan Goodwin climbed the tower on Memorial Day in 1981 wearing a homemade Spider-Man suit to bring attention to the difficulty (or complete inability) of fighting fires in high-rise buildings.