The flaw with that statistic is, that it includes aid to countries like Isreal, which is not an "underdeveloped country" thus distorting the numbers. Aid like that is not a result of the altruistic goodwill of the USA, but merely a way to preserve own interests / protect investments.
Still if you sort and rank the numbers from
http://webnet.oecd.org/oda2009/ by ODA/GNI the USA is still at the bottom with quite a difference in % to the top countries and far from the UN ODA target of 0.7% of GNI.