I think pianists need a more flexible hand. The passing of the thumb under the hand, as in basic scales requires flexibilty. I can do some freaky things with my hands away from the piano, and I have seen many other pianists do freaky things as well. The meain difference is in the muscle development. Pianists tend to have large musculer development along the sides of the hand, and around the thumb.
Flexibilty in being able to stretch the hand is very important. I know lots of people who are not pianists, and are taller than me, and have a much smaller span than me. Not just between 1-5, but between 2-4, 2-5, 2-3 etc...