who does it? I, for one, do. Because I don't have the wing shooting skill that most others have, I want to ensure a clean kill. I admit to shooting and wounding ducks that I prolly shouldn't have shot at. and thats the reason I shoot sitters. me and my friend often have competitions to see who can get the closests to a duck or group of ducks, after the first shot the other (who is waiting about 40 yards back) rushes over and tries to line up his sights on any of the remainding ducks (mainly if there is one that might have taken a couple stray pellets) anyway, makes for some good clean fun and good clean kills.
I know in oregon it is illeagle to shoot them on the water (except maybe if you are using a bow???) but I can't find anything in the regs about that up here