I'm not sure if this is true, but I heard this today at church:

Until very recently, women always had the buttons on button-up shirts suitable for left-handed people who dress themselves.

Legend has it that rich women used to have their servants dress them. So it was easier for right-handed servants (who would stand on the opposite side of the shirt) to dress the rich women if the buttons were set up that way.

Men have always had their buttons suitable for right-handed people who dress themselves.