Was on a mile run to PMW earlier this week and wanted to catch an earlier flight back to avoid the building storm at ORD. Called Premier Exec, and they said it'd be $150 to change.

Walked up to the gate, which was boarding the next flight out, and the GA got me on the flight with no fee. Not that I'm complaining, but is it common GAs can accept later-flight passengers on a space-available basis, while reservations must charge the change fee?