I'm not sure how common book tours are. I've done some book signings at events where I've nudged the event organizers into buying some books and giving me a table to sign them at some scheduled time. (Pro tip: It helps to have someone high up in the event hosting organization quoted in the book :-))

But my impression is that publishers are pretty selective at sending authors around the country on a book tour these days. Obviously big time (or even big time genre) authors can often book pretty nice speaking gigs if they like.