I respectfully disagree... the overall corruption model is not necessarily modelled on United States democracy, I'm afraid.
My take on the corruption model is as follows: in any situation with a ruler who has absolute power (which, remember, in Civ you do), his deputies and the government in general are to some extent kept in line through fear, and the watchful eye of the leader/dictator/whomever. Obviously, the farther a government institution (in Civ's case, a city government) is from the capital and the leader, the less watchful it is possible for said leader to be. As a result, self-interested and corrupt bureaucrats have an easier time getting into positions of power the farther away they are from the capital.
That makes the most sense under a Despotic government, or even a monarchy. Communist governments are irrelevant to this discussion, since they follow their own model of corruption. In my view at least, 'realism' charges are slightly more credible under a Republic or Democracy, but still essentially ungrounded, given that in Civ you have to bear in mind that whatever government type you chose, you ALWAYS have absolute power. You always retain that despotic element, from day one until the end of the game. As such, the corruption model makes sense... at least to me...
