The man is responsible for making the decisions for millions of people. the decisions that they lack the ability to make on their own. Because he saves so many, surely he deserves a special lifestyle.
His vacation budget could also be looked at on a commission basis. Obama essentially earns a commission on the money he takes in from those who have more than their fair share. Thus, he takes in billions for the poor, and he deserves a cut for his efforts, much like the COE of the United Way earns.