Well, to be sure its a lot easier to notice the mistakes in a classical concert. Debussy said that music is not the notes, but the spaces between them - something few, if any, rock band ever get is spaces between the notes. At the level we insist on limiting them to in our venues (A puny 110 dbs, C Weighted - which means at the BACK of the room*) its hard to hear anything other than the din. I think people going to classical music are more aware of the nuances in the score too, and many play some instrument at some level - which also changes the deal.
I work with two symphonies, one world class, the other, a part-time local/regional deal. I can hear the difference between them in a second and a half.
*db is a measurement of sound pressure. Like the Richter Scale, its based on exponential math, so 80 db is 100% louder than 70db. For reference, a jet airplane taking off directly over your head is about a 90db, so @110db we're talking 200% louder than that in rock shows- and, at that, bands get mad when we tell them to turn it down to that. The loudest I've ever measured was 117db, Trent Reznor and Nine Inch Nails.