Expectations Shmexpectations

I hate, hate, hate when people evaluate a politician's performance by comparing how he (or she) really did to how he was expected to do. In fact, I'm going to go out on a limb here and say it's one of the--if not the--dumbest bits of analysis one could engage in. Who cares if Palin was expected to royally screw up and she only kind of screwed up? Who cares if Biden was supposed to win by a mile and actually only won by half a mile? What happened to objective values in these situations? Don't people realize that these expectations are manufactured by the politicians themselves in advance? Doesn't it seem perverse that one campaign has to try to raise expectations for the other side's performance in order to secure some sort of relative performance victory? I don't think this will ever make sense to me.