Other interesting questions: How much of that is profit? Relatedly, does it cost a prohibitive amount to have a highly successful youtube channel? Does amount spent on production each month correlate with amount earned, or do consumers care much more about the content than the production quality?
What is the median income of the top 1000 channels? What's the overall median income of active youtube partners? What's the median income of channels produced (primarily) by a single person?
Some of these questions should be answerable by looking at available stats, like views for the top couple of channels versus the lower end of the top 1000. (Are the actual channels in the top 1000, preferable ranked, available somewhere?) I'll see if I can answer any more of them in the morning...