Live, in media land, means real. It means what the audience member sees and hears in concerts is what is happening right there and then--not what happened in the studio six months ago. For a concertgoer, it means that the interaction between the person on the stage and the audience is genuine, not contrived, not premeditated.
Backing vocals are the antithesis of what a "live concert" is supposed to be about. As a consumer, I already paid upward of $10 for the album or cassette that made me think the performer was worth going to see live. If Headlee thinks I am not being hoodwinked by having to pay upwards of $25 to hear that exact same music at a so-called "live concert," he is only demonstrating his own lack of integrity.
Real artists, the people I pay to see perform, would never give me anything less than authenticity. When is the last time Sting, U2, Prince or 10,000 Maniacs used any kind of backing vocals or taped instrumentation? Tina Turner, Paul McCartney and David Bowie are old (in rock 'n' roll terms, of course) and their voices aren't all of what they once were, but when you see and hear them in concert it is truly them.