I thought that the point of a steep seat tube was to allow for a very forward body position like TT riders use with aerobars. In order for this to be comfortable and for power transfer to work, the BB should be farther back than other bikes. This effectively increases the angle between the torso and legs.

But I could be wrong. I don't think that a steep seat tube would have anything to do with handling besides the fact that it is oftentimes built so it is parallel to the head tube which has a lot to do with handling. So most bikes with a steep seat tube just happen handle quickly.