I'd say it is over-optimization, but I'd agree that this is not the biggest problem. What drives me nuts a lot more, is that the same legs of flight cost completely different amount of money depending where they originate. Try e.g. selecting a flight say from LA to Frankfurt and back and then try selecting flights from Frankfurt to LA (such that legs each way overlap, so effectively it is the same seat on the same plane). Then you'll see what I'm talking about and how the US customer is royally shafted.