I kind of figured about the slope thing, but it seemed easier out of proportion to the amount I swerved, just so long as I was leaning one direction or the other. I thought it might be some sort of skater's effect, where the side-to-side motion conveys some propulsion effect.

I agree about swerving on roads in general. Rock Hill is a bit special, since you can see all cars on it from 50 zillion miles away, and my swerves are not more than 2 feet in either direction, and the traffic on that road is about one car per minute on a busy day. When it gets warm again, and I get myself back in riding shape, I want to train myself to get up that hill straight, with minimal granny-gear grinding, and maximal standing-stomp storming!