With short exposures, dithering every frame is a waste of time. I recently shot IC1396 and used 30 second exposures. I had 80 frames each of RGB and 450 of L. I dithered every 4 frames for the former filters and every 10 frames for the latter. With this many subs I had no correlated noise in the final integrations. I would have lost almost 40% of my dark sky time if I had dithered every frame, but instead only lost 15-20%.
For longer (and fewer) subs I agree... every frame is a must.
Not trying to start a debate as it looks like that has already been done.... just stating my case and why I would find this useful for the developers. 