If I'm paying money to go to a concert, I want to hear them sing live. I don't give a damn if it's perfect or if it sounds exactly like the recording. In fact, I don't want it to sound like the recording! I want to hear differences in the song, and sometimes an entirely new take on it. And I do want them to sing! If I wanted to see someone dance, I'd go watch the 'So You Think You Can Dance' show when it comes around. As far as I'm concerned, if they aren't singing live, I deserve my money back.
In the last few years I've seen John Mellencamp, Bon Jovi, Eric Clapton twice including the last show, the Aussie Pink Floyd show - 6 years in a row, Jethro Tull, Yes, and many others. Every show I've seen featured live performances and live music. If these rock bands can sing and play live, why can't everyone else? The answer is that they are talentless hacks who can't carry a tune without a computer controlling their voice in the studio. And what's the difference between a Broadway musical or an opera and any other LIVE performance? If they are going to charge the outrageous prices they do for a live show, they can damn well perform live!!!
If I want to see great dancing all I have to do is go to Salsathèque on a Saturday night and watch some of Montreal's best dancers tear up the dance floor instead of spending hundreds of dollars to see Britney and Madonna and company's pitiful moves.
Phil Collins said it best when asked about lip syncing...he said "If you can't sing and dance at the same time, then don't dance."