I checked the graphs on your blog. But I wonder if the absence of anonymous edits on the Hindi Wikipedia really is strikingly low? Comparing the number of anonymous and registered edits in Janurays, the quotient is 3.64 (61%/19%) and 6.14 (43%/7%) for the Russian and Hindi Wikipedia respectively. That is, they agree within a factor of 2.
It is true however that the ratio was much higher for the Hindi Wikipedia during most of 2009. But according to the graph, the high number of registered edits seems to be the anomaly rather than the low amount of unregistered edits.
To me it seems much like a vissual illusion that the graphs signals low amount of unregistered edits on the Hindi Wikipedia. The high peak in the cumulative curve presses all other curves closer to the bottom, and the high amount of bot edits does the same for the registered and unregistered curves. If bot edits would have been excluded and the normalization would have been done against the cumulative value in January instead of the peak value, then the curves would not seem to be as different.
By the way, is there anyone who knows what happened about three years ago when so many projects seems to have plateaued.
Thanks for this analysis! It's mirrored some of the work that PARC and others have done, some of which is on this wiki. Philippe is currently undertaking the Herculean task of merging all this work into one place, and I hope he'll include this as well.
Regarding your question about plateauing project participation: This is the great unanswered question. The best hypothesis I've heard so far: the worldwide economic downturn.