I think they influence the show plenty - especially Simon. I'm not saying they rig the vote counts (which I don't think they do, because if they did and it got out, they would alienate their entire viewing base - destroying their credibility and ENDING the show) - but there are plenty of indirect ways to push their favorites. Have the camera pan a little longer on Carrie, have Bo sing a little longer... or more indiscretely, have Simon pronounce that someone will definitely win.