It's more about creating a "production" or elaborate set with a bunch of choreography in most of these pop star performances than singing live. But let's be real here, the amount of dancing a Chris Brown or even an Usher does in their performances it would be extremely difficult to sing live and actually breath while doing all of that dancing and I mean dancing hard. I have a bunch of respect performers like Beyonce and Tina Turner because she gives the people a show with dancing bit not so much that she can't deliver a great live vocal performance too.
1:40 til the end of the video. Justin makes it look easy.