..and many that died young. I wish I had a chance to see Steve Marriott live; had tix for Lynyrd Skynyrd for the Street Survivors tour that never happened, but I did see Rossington-Collins Band twice.
I do cut some of my fav bands (like Kiss) some slack given their age, IIRC, Sinatra was still selling out shows until the end even though fans knew he was a mere shadow of his former self. To me it's a matter of respect, paying tribute and respect. If these musicians played here I'd go see them live for these reasons, not expecting them to sound anything like their prime. Compassion, respect and honor for who they are, their talent and what they accomplished. Same for DLR, though I do have hard time with Vince Neal.
One band that comes to mind where the fans rag on the singer is Dream Theater; James was great in is prime, and I'm happy he's till up there doing it, I don't expect him to sound like he did 20+ years ago, but he's a big part of what makes DT DT to me.
YMMV