I'm not sure. I'm not an LS rep. There is probably some overlap, where the new model is phased in and the old is phased out. I think LS is in that transition phase right now, and who knows how long that might be.
Don't think that just because its being replaced that the XR series tractors are junk. They are still very capable tractors. The new versions just have some new bells and whistles. Just like trucks, new body design, new engine perhaps, new interior layout, every few years. Nothing wrong with the old ones, but everyone wants the new shinny penny.