Don't fret H. You're better off as a gear head than a lot of engineers I know. As for ball bearing...your CV joints have huge balls
And now that you are looking for deeper meaning...
F=P*A is good no? As yelcab pointed out, a circle is a very efficient shape for max area for a given perimeter. Maximizing the area for the pressure to act upon while keeping the shape compact is important...but then we go back to maufacturing...or rather packaging for the masses
