I can't understand why anyone would prefer downtube shifting over stem for commuting. I've heard of racers shifting with their knees, but that can't be relevant. Shifting from the drops is far less common or essential when cruising along, and stem shifting involves less reaching and bending, less interference with your knees while pedalling (if bike is a little small). Stem shifting is really convenient when slowing down up a climb, and is probably the only important occasion where easy and fast shifting is important in a commuting setting.