Perhaps the situation is different in Holland and the USA, but I know for a fact that favoritism towards party members, relatives and their friends is very common after elections among higher ranks of civil servants, both in Austria and Greece (where it was common in the 80's to "recolor" large parts of the public sector when the ruling party changed). This weakens the "static bureaucracy" hypothesis in my book.
As others have pointed out, the POTUS directly appoints many key people and therefore cannot be completely powerless to actually "change" policy (assuming there isn't a closed pool of like-minded people to choose from).