lucy, in a perfect world, you are of course right - the thing is, most of the people there are shoomzers of the first degree and do actually generate a lot of charity money - there will always be the 'have bugger alls' and the 'have too bloody much', just keep trying to part the latter from their money to give give to the former and sooner or later everyone may have the chance to drink clean water.
individual 'celebs' are not responsible for the poor of the world, governments are generally to blame for keeping people poor, down-trodden and ill educated.