It's all how you define "greatest of all time." Nolan Ryan was probably the most exciting pitcher of all time. He was certainly was one of the most unhittable pitchers of all time and one of the greatest strikeout pitchers of all time. And yeah, striking guys out is a goal of pitchers. Strikeouts are better than balls put in play.
Of the guys on the list, I don't know enough about Johnson other than looking at stats. I can't bring myself to vote for Clemens, even though he probably was technically the best pitcher. I love Maddux, but I'll take Nolan's Ks anyday.