Maybe the reason why that isn't part of the criteria is, wouldn't a varied playlist only matter if the artist plays in the same city more than one night in a row? Most artists don't play in the same city for more than one night in a row, so this would seem to be not applicable for most artists.
Was Petty the opening act when you saw him? I'd think a headliner playing in the same town 2 nights in a row would have more reason to vary his playlist than the opening act, because more people would come to see a headliner 2 nights in a row than to see the opening act.
Petty was the headliner, PJ joined him to open for 3 different cities...all of which they played 2 nites in a row...As far as I know, alot of the bigger bands on this list play the same city in a row often...especially the bigger cities...Led Zep's famous show's at MSG in '72 as well as LA/LongBeach in '72.
Why only should it matter if its the same city? I would have guessed lots of people on here would go see bands multiple nights in a row, but i guess I could be wrong.
"A lot of the bigger bands" would be a minority of the list.
I'm not sure, but I'd think that if an artist played, say, Chicago one night and Cincinnati the next night, there would be very few people who would attend both shows, unless it's the Grateful Dead.