I never understood the argument that it's easier to swing a weapon with the arm on the wall-side. On the wall-side, there's wall everywhere, and closes in both behind you and in front of you. On the newel-post side, the space opens up both behind and in front, which seems like it would make it a lot easier to manoeuver a weapon.
For the person facing up, their opponent is to their right, which is closed off. They would need to reach up and to the right, and that motion would be blocked by the newel post.
For the person facing down, their opponent is to their left, which is open. They would need to reach down and across their body to the left, unobstructed.
This is the first time I've heard of this and I don't quite buy it either. Having your left side on the wall side also means that you can stabilize yourself against a handrail with your left hand.
