It needs a minimum of 80 votes to get on the list. When a film first aquires 80 votes, most of the people who have seen it are people who were attracted to the subject matter and cinematic style. People who aren't so attracted to the themes or style of City of God will be encouraged to see it because of it's high place in the top 100. Not being so into COG's particular style they are likely to rate it lower than those who have already seen it. I predict that a month from now, COG will have droped out of the top 10.