You frequently see this when you look at concert lineups and wresting/boxing/mma cards. Sometimes things happen and people are unable to perform. Usually its understandable and the booker of the event will attempt to alleviate the disappointment by having someone else fill in.
Yesterday I attended Ozzfest in Camden. The weather was pretty bad at times with heavy rain and the threat of thunder storms. Still my friends and I did not care about getting soaked. We were attending Ozzfest for one reason and it was to see Black Label Society. Unfortunately as Black Label Society was due to close the Second Stage (outdoors, not in amphitheater) the weather worsened. People were told to take cover and that Black Label Society would open the Main Stage. Except after waiting about 45 minutes to an hour, Black Label Society did not perform. No formal announcement was made. Conflicting information was provided by roadies. Apparently the rain had damaged some of their equipment. The band we were dying to see didn't perform, not even for a couple of songs. Nothing was done for the customer.
Today, I find out (unconfirmed) that BLS was prepared to play with borrowed equipment but Live Nation had a schedule to stick to. Obviously the day was a disappointment and all we got were soaked clothes and a shitty performance by Rob Halford. I'm not sure who to blame but the customers were fucked over.
Live Nation is surely to be blamed for another issue though. Parking was advertised to be free. It was the usual $25 cash grab. They are supposed to be issuing refunds now but I'm skeptical. I certainly won't be going out of my way to attend any concerts at the Susquehanna Bank Center anytime soon. Overall Ozzfest was poorly organized and I'd say it was my last one if I wasn't so sure it was officially dead anyways.