Acceleration and Velocity

This is a video of the 2008 Olympic 100 meters finals in Beijing. This race shows acceleration because starting out of the blocks a runner must speed up by changing his velocity. If you noticed in Usain Bolt's last 20 meters when he knew he was going to win he stopped accelerating and driving, but he was still going the same speed. How is this possible? Usain Bolt decreased his acceleration yet his velocity stayed constant, thus allowing him to when the 100 meters .2 seconds before everyone else.