Actually, this might be the truest representation. This graph applies the ratios in the previous graph (total plays / # of unique songs) back to the total number of plays, essentially weighting the total number of plays based on the number of unique songs in each group. I think this is more what you were getting at, @hamburger_helper, and may be the most accurate way to look at it.

At least I think. I've always sucked at math and never took statistics.