I believe Terry has said that most names in Discworld can be found in an average telephone directory. But it's certainly possible that Ken Weatherwax's name may have stuck in his head (just like the name for Rincewind did). Another theory is that he got the name from the Weatherwax Family famous for training K9 filmstar, Lassie.
RIP Joe Cocker
Billie Whitelaw too? What a wonderful actor. I saw her at Newcastle Theatre Royal, possibly late in 1965?, playing Desdemona to Olivier's Othello (we were studying the play for A-level Eng Lit). Ms Whitelaw was on stage due to the fact that Maggie Smith was unwell. Bloody fantastic performances all round.
So sorry you're not with us any more Billie