Here is a nice article (via The Browser) theorizing about why Wikipedia works.  The apparent puzzles are why people contribute to this public good and why it withstands vandalism and subversion.  The first puzzle is no longer a puzzle at all, even us economists now accept that people freely give away their information and effort all the time.  But no doubt others have just as much motivation, or more, to vandalize and distort, hence the second puzzle.

The article focuses mostly on the incentives to police which is the main reason articles on say, Barack Obama, probably remain neutral and factual most of the time.  But Wikipedia would not be important if it were just about focal topics that we already have dozens of other sources on.  The real reason Wikipedia is as valuable a resource as it is stems from the 99.999% of articles that are on obscure topics that only Wikipedia covers.

For example, Barbicide.

These articles don’t get enough eyeballs for policing to work, so how does Wikipedia solve puzzle number two in these cases?  The answer is simple:  a vandal has to know that, say, John I of Trebizond exists to know that there is a page about him on Wikipedia that is waiting there to be vandalized.  (I just vandalized it, can you see where?)

There are only two classes of people who know that there exists a John I of Trebizond (up until this moment that is.)  Namely, people who know something useful about him and people who want to know something useful about him.  So puzzle number 2 is elegantly sidestepped by epistemological constraints.