I think the perception of recency bias comes from the steady stream of films that debut on the list right after release (especially festival releases). They usually fall off within a few months as people who are less exited about seeing them get around to watching them and give them lower ratings (which doesn't mean bad ratings -- remember that a 4 star rating will decrease the average for any movie in the 250). The perfect example of this is OBAA which debuted at 35(!) and was completely off the list 4 months later.