As far as I know (but correct me if I'm wrong) the first time blast was used as an exclamation was in Star Wars, and there was a good reason for it. Blasters. It just isn't WoT. And Sanderson just said "blast" in his twitter, so it's just a word he uses. I had a friend who said it a lot too. It's a popular word for nerds. Not something people would use in WoT, imo.