Osama bin laden was very useful for the USA. It could bomb at innocents in the name of Osama. It could wage war over new territories and countries citing the name of Osama. It could tear apart the sovereignty of far away lands at will invoking the name of Osama.
It could allot billions for the war over terror using the bogeyman of Osama. It could promulgate stringent laws, It could humiliate and strip search the leaders of third world countries, It could hoodwink its public - everything in the name of Osama.
That is why the hawky bush and his poodle Mush kept the golden goose alive and kicking. Remember how a video casette released in the name of Osama on the eve of elections swing the prospects of Bush? Then why did Obama got Osama - the golden goose - killed?