(Click here to see an ArgusLeader.com video of the failed implosion) SIOUX FALLS, S.D. -- Thousands of spectators gathered Saturday to watch the demolition of the city's tallest building - but the Zip Feed Mill tower was stronger than it looked. The 202-foot-tall concrete structure dropped slightly, leaned a little - and stopped. The abandoned feed mill elevator in downtown Sioux Falls paled in comparison to structures such as Chicago's 1,450-foot Sears Tower or even North Dakota's 242-foot state Capitol in Bismarck, but it was widely considered the tallest building in South Dakota. That was enough to draw people outside,...