I have to agree, going from PS/1 to PS2/3 was a big jump, and it's no different than Lionel going from conventional to command. After all, when Lionel introduced TMCC, you had to buy extra hardware to run conventional equipment with their TMCC system. MTH had a box that ran conventional equipment, including PS/1, without buying anything else.+
In either case, if you already had a conventional transformer, you could run either system with no added equipment for conventional operation.