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#edit…
, or something more compact like Gini factor.
Nemo