Actually, I used the average rolls for that.
Why wouldn't they? It's good damage on the charge at first round or surprise round, and since you can just let go off a 2-handed weapon with one hand as a free action and grab it again as a free action, it's nice for making AoOs and attacking when the enemy is not flat-footed. We're assuming competent players, no?
7 ranks + 4 via Cunning Knowledge + 10 average d20 roll gives 21. You need 20+ for 3d6 damage.
RAW implies monks aren't proficient with their fists. Also, there's the Sage's ruling for what it's worth.
I'm using a rather generic martial factotum with perfectly average rolls, and I don't see where this "very lenient DM" steps into the picture.
Why on Earth would he use short sword? Seriously.