I think that, at least insofar as it pertains to Billy Joel, he was at least honest and continues to be transparent about his status. He doesn't have anything else that he wants to say and is quite happy playing at MSG and doing his thing (I saw him a couple of weeks ago in Hyde Park. It was one of the best gigs I've been to). The issue with GNR is that members (and historically, Axl) have dangled the possibility of new music, but for whatever reason, it very rarely materialises.
I personally have no issue with GNR being a nostalgia or legacy act; I won't be seeing them again in any event so it's all the same to me. I also don't particularly care whether they release new music or not but I do empathise with the people who do care or for who, new music is a condition of them seeing GNR live again.