As far as I can tell cheapish 2D lidar for mapping and robot navigation were a bit earlier than the XV-11; they were made by Hokuyo in 2006. I remember that their lidar module was made by some other (American?) company that in turn competed with Hokuyo, people would take them out and use for their own projects.
It's ultimately not very complicated - it's a laser rangefinder that you spin on a motor. It's such a simple - and old! - technology which would obviously get significantly cheaper with time, it was definitely the right horse to bet on. I never understood iRobot's vision strategy.
