Interesting that just last night I was picking brains (well, there were only two sadists present) in a chat room. Interesting too, that research expounds on the "receiver" of pain (their motives, their emotional well-being, etc.) and has little information regarding the "giver."
I'm not at all surprised that the number of men into BDSM tops the percentage of women. Could be that you're surprised because there are definitely more submissive females/males than dominant female/males that practice the lifestyle.