As opposed to say...a forum, where a bunch of 30-and-40-somethings repair all the errors.

Wikipedia has errors and bias, but at least it
can be edited or discussed, unlike a page that
never gets updated. Not many websites ask you to provide a source, either.
Professors and teachers didn't like it if you copied World Book Encyclopedia word-for-word twenty years ago, either. When my wife taught high school, she'd give Ds or Fs to those who blatantly copied and pasted from the internet, 5 minutes of research doesn't count for a grade. Why then, are people so surprised that Wikipedia is not considered a primary source of information?
Wikipedia itself claims it is not a primary source of information.
If you've read at least 100 articles from WP (and we've probably all done it at some point or another), you can easily spot the difference between a well-contributed and informative page, and one that is heavily biased, or a page that descended into stupidity and becomes a fanboy's delight. You can see who's edited the pages, who has approved the level of accuracy and value of contribution it has to related WP pages. You can see footnotes, sources, and how many statements are out of place.
If you know a thing or two about the basic policies of Wikipedia, then you should be able to spot bias right away, and dismiss the BS from an expert with a B.S. Wikipedia also has many bots that look for certain words, and revert vandalism right away. The most childish and immature of edits are quite obvious to spot, and can be reverted (sometimes in the blink of an eye). Other drawbacks are the very tough policies they have in place for article contributions and additions, coupled with my opinions that a wiki is probably the world's worst computing application for discussion between individuals, since it too, can be edited.
[citation needed]
People are quick to dismiss Wikipedia, but usually they are not armed with the facts and do not have a little bit of experience in editing nor contributing to it. No, it is
not an all-encompassing source of information, and no page intends to entirely blanket a subject and present all sides (although some are really darn good at it). But with a little knowledge of the expectations of WP and how and why it works, and what it intends to do, it is quite hard to beat as an internet-based reference tool.