Seperation of power (http://en.wikipedia.org/wiki/Separation_of_powers), but even so they are picked indirectly by the public through politicians. As a european though I am pretty amazed by all the direct voting that is done in US - you can hardly drive through a town here without running into a plethora of posters for people campaigning for various offices. You could argue that this is good democracy but I just can't imagine how voters can make informed decisions when voting for all these various offices - that is if they even bother to vote.