Actually, it's just been my own personal experience that when I shoot a lower-spined arrow, my point of impact moves to the right, shooting a fletched arrow, right-handed. That's why the passage from Asbell's book always stuck in my mind, and I knew immediately where to look for it when I read Old York's opening post. I always thought it was an error, but given that other people's experience agrees with Asbell's comment, maybe it wasn't an error.
I don't know why increasing spine would cause some people to shoot to the right and others to the left, but I am very curious, and perhaps one of our "guru's" has an explanation.
I ran across a similar thing having to do with bow tiller. Mostly, when you ask a bowyer how he tillers his bows for 3 under, he will say that he puts less of a positive tiller on the bows he makes for 3 under. For example, if he puts a 3/8" positive tiller on a bow for split fingers, he will put a 1/8" positive tiller on a bow for 3 under. Black Widow does the opposite. They put a greater positive tiller on their bows for 3 under than they do for split fingers. Why, I don't know, but it works for them, as much as doing the opposite works for others.