Singers Cheating

When we pay a considerable amount of money (as opposed to buying the CD) to listen to a singer live, I think we are cheated if and when a singer gets to the highest note of a song and lets the audience sing for him/her. Why doesn't anyone walk out and demand to get their money back? If a singer deems the song is too high, they can always transpose it to a lower key, so that they don't strain their voices and don't have to cheat the people who paid to see their performace either.