the ruling party benefits from the oil while the other parties within the nation do not. those countries are generally composed of tribes of muslims. the ruling party is the tribe which has the most power. and some of these tribes are not exactly friendly with each other. this is the cause of many civil wars within a country, and explains the situation with respect to genocide in iraq. this genocide is not limited to iraq or countries in the middle east or muslim nations.
so in such countries, the rich truly do get richer, the poor get poorer. there is no "socialism" there to spread the wealth.