This is all I've been thinking about as I plod along today out in the yard...

Had an insight:

The metric system is decimal (deca, 10, etc)... Base-12 (for lack of a better term) is about fractions. And fraction is really another word for proportion. Daisy wheel is all about proportion...the number 12 is a very divisible unit.

And as Derek points, Davinci's wheel must be related. The human body was likely the base of measurements, or the proportin of certain body parts. Remember that originally an inch was supposedly the length of a man's thumb: the nail to the first knuckle?