CAS,
In the days of yore, a gentleman was always armed, a social responsibility thing. The weapon/strong hand was never restricted. With 7/8ths of the population right handed, that meant that the wallet went on the left. IIRC Most breeches didn't have front pockets till way into the 1800's.
It is also why ladies and subordinates walk to the left of and slightly behind, to allow free access to weapons on the part of the gentleman whose duty it was to take care of any dirty work. Also why hats were tipped with the left hand when meeting with ladies allowing weapons free as needed, salutes and hand shakes with the right with gentlemen, depending on military status to demonstrate friendly status, ie. no weapons to hand. It also follows from there, one of the reasons why left handers were looked upon with some suspicion.
Sam