Yes, it's a sad reflection on these technologically 'advanced' times that people see fit to 'cheat' an audience in this way.

However, I recently saw Hamish Currie at Saddleworth Folk Festival using a digital 'loop' machine. He played his trumpet into a microphone, which recorded the melody into a pedal box. He then hit another pedal, which played that back whilst he recorded a harmony. He then added a third recording, which was then played back whilst he sang.

Rik Saunders of Fairport does a similar thing, as I recall. But the difference is that these two people are actually playing live.

This practice was originally pioneered by the late Les Paul, of course.