Its not easy to make a controller work from 24v to 72v.
Sure I can do 48v with my 72v controller but it runs like a little girl at 48v starts to switch nice at 60v and kicks arse at 72v.
Its hard to get the threshold of the fets like a hair trigger over such wide voltages.
You will notice large differences in performance when you mix and match parts. A simple bias zenner between source and gate isnt absolute and one needs comparmise performance for compatability.
Possibly you will be able to use 72v but GM just maybe not advertising this and you push the controller at higher volts at your own risk.
I for one do not care about going faster I just want a 48v controller that can go higher volts than it is intended. By using such components like 100v fets on a 48v controller you make the controlller almost bullet proof. I am hoping that this is the case with the new announcements.