The TurtleBot uses the ROS navigation stack. The navigation stack requires a 2D laser scan to work. To create a 2D laser scan the kinect point cloud data is converted to a laser scan using the pointcloud_to_laserscan package in the turtlebot stack.
The pointcloud_to_laserscan package contains a nodelet called cloud_to_scan which samples the data in a region around specified height in the point cloud. Then given a set of points in an angular slice it returns the min range value for that angular slice. See the code for more details on how a point cloud is converted to a laser scan.
The TurtleBot localization primer might also be instructive: http://www.youtube.com/watch?v=C92bxCr05Gs