Although shake is certainly added by the projector, Harmy's corrected for that by stabilizing PuggoGrande to the very-still HD footage, and the subtitles still shook. You're right in saying that the subtitles are burned in, but remember that this burning in process also required running film across sprockets and all that... introducing its own shake. So even if you could run a 35mm print of Star Wars through a projector with absolutely no shake, the subs would still shake, because of how they were made.