You must have missed this little nugget of information based on research released in december of 2005.
http://news.bbc.co.uk/2/hi/technology/4530930.stm
Wikipedia has the same number of factual errors per article as Encyclopedia Brittanica, which until then was seen as the worlds most accurate encyclopedia. Wikipedia simply rocks.
Since then wikipedia has tightened up control and controversial articles can only be changed if your on the comitee, which as a rule are headed by real scientists, (at least I know Swedish wikipedia is, and there's no reason for me to believe it's handled differently in the English one). So now it's even more accurate.
I think chances are pretty good that wikipedia is the worlds most accurate encyclopedia, and research suports it. So there.

There's been more research after this, (funded by Encyclopedia Britanica off-course) that failed to debunk it.
Wikipedia still can't be used for serious scientific research, for obvious reasons of traceability. But it would be foolish to discount it simply based on it being wikipedia.
I think it's secret is just the fact that anybody can edit it. No other encyclopedia has more proofreaders.