Ron,
Take your argument to its logical conclusion; if you ordered tomato soup and were served mushroom on the basis that it is all soup you would (I would) be pretty hacked off.
We go to concerts on the basis of the fact that we know what we are going to hear. If we don't get what we think we are going to get we are being sold short.
Put yourself in the position of a chamber music enthusiast who turns up for a concert to find The New Lost City Ramblers.
If we only listened to the performers we were familiar with, we would never hear any new ones.
Jim Carroll