The MARK VI's started to come on line in 1989, with the final train being delivered in 1991.Back to Disney World. I don't know when the Mark VIs were delivered. I'm not suprised at all that SOP hasn't changed though, and I'm sure that the new trains were not any more safe than before. Why would they have to be after 40 fail safe years? It just means more money.
As for your assertion that the new trains are not any safer than before, you would be wrong. The MARK VI's were built by Bombardier as a production line item. They had hopes of selling them, and therefore the new trains were much safer than before.
Just to name a few safety features, the MARK VI's have a fire detection system, emergency escape hatch in the room, they now fill the tires with nitrogen to reduce the risk of fire (after a fire started by a tire on a MARK IV), and many other things.