I'm not so sure that they're all asymmetrical. Shimano 113's are symmetrical, as are 107's and 103's. 110's are asymmetrical, with the drive-side axle being the same length as the 107, and the extra 3mm being added on the non-drive-side.
I started a thread awhile back in attempt to catalogue symmetry and asymmetry of sealed-cartridge, square-taper BB's.
http://www.bikeforums.net/showthread.php?t=196235