I suppose I should have mentioned this to Ben himself actual, but something struck me about his findings, especially finding 3, "Wikipedia attracts contributors because it offers low transaction costs to participation."
I think that needs modification. As Grimaud has discovered, "low transaction cost" is not quite precise enough. In Ben's analysis, Wikipedia offered low transaction cost relative to the other options on offer. There's no reliable "absolute" measure of transaction cost as lots of it is tied up in HCI issues. In our case, it seems that Wikipedia has a relatively high transaction cost in relation to other forms, especially for anything more than trivial or minor edits.
Incidentally, thanks for posting all this. Potentially very useful! Stephensd 10:27, 17 August 2012 (UTC)