I suspect a neurochemical basis for this - when one is rich and in the higher echelons of society, it goes to reason that their brains will have more serotonin swimming around due to a) better food and b) more socialising.

Having higher levels of serotonin makes us more blind to unfairness:

http://www.sciencemag.org/content/320/5884/1739.abstract

> We observed the effects of manipulating 5-HT function on behavior in the ultimatum game, where players must decide whether to accept or reject fair or unfair monetary offers from another player. Participants with depleted 5-HT levels rejected a greater proportion of unfair offers, but not fair offers, without showing changes in mood, fairness judgment, basic reward processing, or response inhibition.