I guess it's true. some acts sound so bad live that they have to mime. Live music doesn't make the transition to tv to easily so it's usually the case.
Although i remember one incident with Iron Maiden in Germany, they were told to mime and refused to do it. They suddenly agreed at the last minute with huge cheesy grins on thier faces. they went on tv and started miming, after the first verse they all just stopped and swapped instruments then just carried on as if nothing had happened, all with the wrong instruments!
I may stand corrected on some points but basically that's how i remember it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ One by one the pigeons steal my sanity.
Of all the things i've lost it's my mind i miss the most.