Sorry, double post: the "Revisions per author" is not explained either. If reflecting the previous graphs, it's just a division of number of revisions by number of authors so I don't see how it adds any information. If the aim is to complement raw totals with some hint of the community health, you may want to graph distribution of edits data such as http://stats.wikimedia.org/wikispecial/EN/TablesWikipediaMEDIAWIKI.htm#editd... , or something more compact like Gini factor.
Nemo