there's a difference between a "check" and a "roll". the physics check is determining "is there an enemy in the way of my weapon". To perform that check, they probably compare coordinates of both people considering weapon type and facing.
A roll is much simpler, computationally speaking.
You're also forgetting:
removal of the .15 second timer/procedure request (we don't know which it is) between physics checks.
I have reservations about the % chance of off-hand strikes thing (ie: the nerf), but the other parts of the proposition (replacing some alacrity with double strikes, removing redundant physics check) sound great to me.