That's odd.
As has been mentioned, it's against the law to go on the pitch.
The Bizzie's must be incompetent to only arrest two people from the thousands that were on there!
Maybe they already have the Christmas fund topped up, so didn't need the extra money from fines? Or maybe it's not that much of a big deal at the end of the season? Besides, does that law even count once the season has finished - it'd be pretty weird fining thousands for being on the pitch during a take that concert.