Re: "The Boss"??? Not the boss of curfew laws!
Some comments in the article make me wonder if the performers did know about the curfew. They broke the curfew time by more than 30 minutes, that's not a minor "last number and say goodbye" thing.
So there are a few causes possible:
#1 They didn't know exactly when the curfew was or how strict the curfew was.
#2 They didn't care about the curfew.
#3 They wanted to generate press noise for general promotion.
As I know it, stage times (on and off) are the only law at festivals, a lot of things are subject to negotiation, stage times are not. Why should it be different for the Boss and Sir Paul?
The guitar player's remark about breaking curfews all over the world leads me to believe it's #2 and #3 in play here.
The mayor's remark is very dangerous, as future curfews would have suffered from this. There's no use in issuing a curfew when it's not followed, regardless of who is on stage. The mayor could have worked towards a later curfew in the first place, let's say midnight. I suppose they would have played until 0:23 or something then.
Bottom line: Strictness of curfew times should not depend on the act on stage, it would be unfair and lead to some trouble at curfew'd shows with "lesser" acts.
EDIT: I suspect the last, last number to be "Hey Jude". A great soft curfew breaker. The band can stop and the audience sings it for quite a long time...