Well not to confuse the subject anymore than need be, here is the answer from the B747 side of the house. The B747-Classic was never certified for CAT lll so the DH would have been 100' "see to land", CAT ll, while the B747-400 is in fact a CAT lll certified aircraft with a 100' alert height (no see to land) FAA rules. As someone has said before this is a function of the autopilot design and certification. Again all of this may look a little different under someone else's certification rules so don't bet the farm on these answers.