I think it is pretty common actually. Unless the commute is hilly, it really makes sense to simplify the bike as much as possible to increase its reliability.

And, even with short dropouts you can probably still get away with a one or two tooth difference on each side of a flip-flop. Each tooth adds 1/2 inch of chain. Half on the top half of the loop, half on the bottom, so each tooth requires 1/4 inch of drop. I bet your drops are longer than 1/4 inch.

jim