One of the reasons for trying the Ultimatum Game in poor villages is that you can see if the theory holds for high rewards, without spending $1,000 a pop to try it out in San Francisco.
This behavior changes as people grow up. As teenagers, people generally won't accept a split worse than 70/30, which implies that it's worth it to lose out on the 30 in order to send a message to the stingy giver. Also, men are more likely to engage in this sort of justice-driven behavior than women, which is all considered economically irrational. But when the stakes get very high they tend to outweigh people's ethical notions of fairness.