Impact of the long tail on blockbuster movie ratings

Flowing Data has a great chart tracking the average ratings of the top ten grossing movies over time.  I believe the clear downward trend in ratings is driven by the ongoing expansion in the volume of filmed media available.  As more and more diverse content becomes available, our frame of reference to evaluate films expands, which logically results in lower evaluations of our common denominator:  the blockbuster.  This phenomenon is occurring all across our economy as more and more varieties of music, food, drink, film, books, restaurants, you name it become available.