You are very right. 15 years ago I was searching for a flat wire rolling mill for magnet wire for a China company. I was told by one manufacturer that they had not made a complete system with 3 vertical stand with 2 edging stands in about 15 years which at that time would have been back to about 1980. Additionally I heard a story true or not about a similar mill in Brazil that had state of the art drives and controls- the irony was that the mill stands were nearly 100 years old at that time.
So like you say, the basic foundation for the machines, Torrington, Fenn, Syncros, Vaughn, and others were so good that they could last forever, all you might do is change types of bearing, improve drives, etc. and increase speed, etc.