I'm just speculating, but I think leather always has some oil/wax like content (unless it is dry, brittle and cracked). I suspect that stropping has several effects, one of which is to coat the bevel with a film that reduces cutting friction (and decreases the draw while stropping).
I recall Torolf (Scrupleworks) telling me that people usually prefer strops with more draw in the beginning and as they become more experienced, tend to prefer strops with less draw. That has also been my personal experience.
