In your opinion maybe. But they have and they do sometimes. I have been rebooked the day before on AS and AA when they have been seriously oversold. AA has even called me the day before, and once three days before, offering me another routing if I would change flights from one seriously overbooked.

The fact they allowed the oversale doesn't mean that they now might not have a problem. They may have allowed the oversale days or weeks ago assuming they would have a certain amount of cancellations based upon their predictions - if those cancellations did not occur they may now be willing to accommodate someone on another flight.

It's similar to the situation when you show up at the airport and the check in agent asks if you might be take another flight . They know that have too many people for too few seats and they aren't telling you to go to gate and wait it out but attempting to reaccommodate you ahead of time. They sold too many seats and while that is usually indicative of a belief that things will work out sometimes their yield management predictions are wrong. The airline usually would prefer to resolve the problem earlier rather than later than to be put into the position of having to IDB someone at the gate.

Finally, even though they aren't selling anymore tickets for the flight doesn't necessarily mean that it is oversold. By calling you could find out if it is really oversold or whether AS believes that everything is just fine and there is no real danger. If you happen to know an AS employee or two that can get on line and look at the numbers also can give you a better idea of what's happening. For example, employees on here have sometimes posted in response to questions about particular flights that they are or aren't oversold even when the flights are zeroed out. Of course, I've also been bumped on a AS flight with six other people (including 2 IDB) when the flight did not look seriously oversold earlier in the day.