I think we have every right to debate topics like these whether we'd question it to their faces or not - it's all part of being a public icon. I certainly don't kid myself that Mick Jagger cares one iota what I think - I'm sure he doesn't, and I'm sure I wouldn't if I was in his place.
No doubt, if people enjoy the music or the show, more power to them, and nothing wrong with that. Being popular and being good aren't necessarily correlated. It's always interesting to see what mix these ageless bands play of their music - I'd bet Neil Young plays a lot more of his recent stuff than many people who have been making music that long, and I'd guess that that is correlated to the quality of his recent stuff.
Here's another way I think about it - what bands am I willing to buy the next released CD immediately for? It's a non-trivial list, but it's not endless. But if The Who was in the middle of their streak of great albums in the 60's or Stevie Wonder's streak of albums in the 70's, they'd both be on the list. In 2006, they're so far off the list it's comical. Whether I am interested or not, I would see reviews of either, because they would be covered in the press, and if they got rave reviews, I'd probably try to hear some of it and be interested. My point is, as great as those two artists were at their peaks, there are so many other bands / artists that are turning out stuff that I have higher expectations for, that they're not all that relevant or compelling anymore.
I don't think there is anything mean-spirited about the topic at all.