Hi Ranger,
I've always wondered about them designations.
And also why RST was used, as opposed to say ABC.
The first time I ever picked up a European Electrical book, it took me a wee while to work out what they mean't.
Our motors use A1,B1,C1 and A2,B2,C2, I think that this is based on the British system, but I could be wrong, too!.