This question has been in the back of my mind recently. It seems like many, like more than you would expect, of the good slalom skiers are RFF. But in any other single board sport (other than mono-skis ;-) ) most people are LFF. In fact, in skateboarding, snowboarding and surfing, RFF people are considered "Goofy Foot." I now here talk in technical discussions of the "offside" turn being "toe side." So it seems to me that the same foot would be forward. Granted, our feet are in front of one another, rather than standing at hip width or so. But not sure why that would change anything.
I have waterskied since I was 9, so I doubt I would try to change anything now. I tend to kick a ball right footed (which I guess some would say I would be RFF, but that flies in the face of the Goofy Foot conventions). If someone pushed me from the back, I would put my left foot out to catch myself. I put my left foot in my pants first (saw that test on the interwebz) and as said, am LFF on any other board.
So, if most people in other sports are LFF, why so many RFF?? Inquiring minds want to know.