If as a fan you invest your time, interest, and money in your musical idol(s) then you automatically feel a degree of ownership, coupled with a sense of entitlement over the music produced, and the way in which it is presented to you.
Unfortunately, this flies in the face of what the artist wants to do, which is develop new music, and find interetsting and refreshing ways of presenting old and familiar music.
That means that some artists do re-vamp their 'standards' to a point where they are unrecogniseable. I am in Canada, and saw Bob Dylan last week,doing exactly that by turning Blowin'In The Wind into a Cajun waltz tune.
Some artists are simply wilful. On one tour, Neil Young, an artist not known for crowd-pleasing, played his new and un-released album from start to finish. He then told the crowd that people moaned at him for playing music they hadn't heard before, but they had heard his new album, and he simply repeated all the songs over again!
I saw BB King a few months before his death, and he was well past the ability to deliver a shadow of his genius as a blues legend. He played You Are My Sunshine for twenty-five minutes! Even his band looked embarassed, and people started to leave.
In those instances, where people will pay to see a legend, it is the responsibility of the legend's 'people', and ceertainly the promoters, to ensure that they legend is not simply wheeled out to destroy their reputation, but is capavble of providing a show that merits an audience paying good money to see.
But part of loving a musician is accepting that loving is not owning, and following does not buy you the sense of entitlement you wish you had - you have to accept what they do, because it's their right to decide what to perform and how to perform it.