You would be surprised how prevalent this is. The flip side is that super high power stage amps haven't been necessary since the 70s, it isn't practical and makes getting a balanced level on stage or front of house almost impossible. Then factor in the expenses of shipping heads and cabinets around on a big tour and the man power required to set them up.
However the iconography of a big old Marshall stack is so strong and embedded in peoples psyche that audiences demand it.
None of this excuses the dishonesty though in my opinion.