I don't see the tractor anywhere on their list. I think it's by far the most significant development. Before the tractor, nearly half the country's farm production went to supporting work animals such as horses and mules.
I'd put the bicycle high up on the list. Regrettably its main social significance was to prepare the way for the automobile. The bike may have also been very important in providing women in general for the first time with the ability to quickly and easily travel away from their houses -- the first taste of personal freedom.