Re Landing Fees:
Last time I was at a Legends meeting some poor sod was told by tower just as he was about to depart that they had no record of his having paid his landing fee and made him return and shut down to pay: despite his protestations that he'd paid he did so, only for tower to confirm he had indeed paid.
Much contrition and apologies over the radio by ATC in between issuing clearances.
So: they do have a link, albeit unreliable from cash desks to tower.
On busy fly-in/airshow days it just would not be possible to have hoardes swarming all over the tower trying to pay their fees.
great day though.
Cusco