There's quite an interesting statistic buried in
there:
"People who've made more than 10,000 edits add nearly twice as many
words to Wikipedia as they delete. By contrast, those who've made
fewer than 100 edits are the only group that deletes more words than
it adds."
This seems entirely plausible to me, but what struck me is that it
doesn't quite seem to gel with the study last year which claimed that
most contributions were from incidental users...
It's difficult to judge that statistic without knowing whether they're
referring to the main namespace, or the whole project. The
"chaperones", as the author calls them, may simply be deleting lots
from the mainspace and adding lots to talk pages and the project
space. The "people with <100 edits delete more than they add" is, of
course, heavily skewed by people blanking entire pages.