Re: **** you, Channel 7!
There are certain parts of the day that are designated for the local affiliates, which is when they sell their ad time. This true in North America, at least. So that was probably what happened.
Really out of the control of the broadcasters. Happens all the time here; for example, with the rain-delayed U.S. Open final on Monday. Lots of local affiliates didn't even show Federer - Murray, if you can believe that. It was on a case-by-case basis.
But it's written in stone in contracts.
ESPN is a sports network that shows the same programming in every city; completely different situation. But even then, if they have a "better" live programming offer than tennis (in their eyes), like golf (rolleyes), they'll sign off at the designated time.