Apple has been releasing data about payments to developers with increasing frequency. Last week’s $5 billion announcement was the fifth such update and came after about one quarter since the last.
Knowing the payments to developers and the cumulative download count allows us to get a very accurate revenue point for each download. As the frequency increases we can observe growth and seasonality patterns.
The following chart shows how average revenue per app download and the average payment rate to developers has changed since the iTunes app store opened and given the data points available:

The green area in the chart should add up to $5 billion. The average revenue for all downloads is 24c.