The other major one, which the article/study perhaps misses, is collaboration. I and others who modify the pages I track will sometimes contribute after someone gets the ball rolling with a change.
However, the study may have accounted for this by looking at the content of these "most sociable editors" user pages. Here's the working paper version of the cited study, which I haven't read yet: http://blog.mikezhang.com/files/chinesewikipedia.pdf
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Also: http://xkcd.com/386/
That's my primary reason today.
The other major one, which the article/study perhaps misses, is collaboration. I and others who modify the pages I track will sometimes contribute after someone gets the ball rolling with a change.
However, the study may have accounted for this by looking at the content of these "most sociable editors" user pages. Here's the working paper version of the cited study, which I haven't read yet: http://blog.mikezhang.com/files/chinesewikipedia.pdf
The same reason they comment on social news sites.