The best rotors in the industry will warp if the surface to which they are bolted isn't flat. As GH posted, the wheels themselves have been suspect for several years now but that seems to be the last thing the typical dealer bothers to check. Much easier to just be part changers rather than figure out the root cause of a problem.
BTW, my opening statement shouldn't be construed to mean that I think Harley's current rotors are all that great. They cheapened them just like they've cheapened many other important parts, and we all know how well that worked out with stuff like crankshafts and compensators. What I meant was, even if you buy outstanding quality aftermarket rotors, if the wheels aren't right you may very well still have issues. Get the wheels checked if you experience warped rotors; it's very easy to do while they are swapping out the rotors.
Jerry