You cant buy a dvd to show you havent been to,they are only available after the concert is finished,so each night is unique if it is a crap concert nobody will buy a dvd of it(obviously you will get the few-collectors)
People will share thats going to happen but no more so than youtube,the average Joe isnt going to be searching for the crap shows.They will want to get their hands on the good ones(providing there is some)
Its always the good shows that get passed around