Not to endorse what TicketMaster is doing -- it's despicable -- but isn't this a case of apples and oranges?
If I had a ticket to see COMPANY on March 30 and the performance on March 30 didn't happen, that's the ballgame. Just because there are going to be future performances of COMPANY (in all likelihood) doesn't change that the specific performance I bought a ticket to was canceled.
But if I bought a ticket to a concert on March 30 and it was rescheduled for December 10, then the performance is still happening, albeit at a later date.