No it's not. It's live, not a backing track, first of all. Secondly, as I said, to open a show the intent is to keep the focus entirely on the band. These musicians are brought out eventually early on (if what you say is true..never noticed..) in the show and there they are, plain as day, singing and playing. No biggie. Jagger even introduces them to the audience during the show, total acknowledgement. It's not pre-recorded backing tracks, they're musicians supporting the band.