Take a look at Snopes once, huh?
Every time somebody says something, it passes through the public mind. Sometimes it gets down five people and dies; others, it becomes an ever-growing ball of horse shit, and people start claiming that it takes 8 pounds of honey to build a honey comb that holds 1 pound of honey when, in reality, beeswax is pretty cheap in terms of hive storage economy.
There are so many untrue things on Wikipedia just by way of almost everyone believing them--things that are printed in earnest in College textbooks and technical manuals, repeated by experts in field, and yet readily testable as not-true. These are just like Aristotle claiming heavier objects fall faster--and, 3000 years later, Galileo drops a grape and an iron brick at the same time, and both hit the ground simultaneously; did nobody think to check something other than a rock versus a feather? Today, we have the same.
To make matters worse, anyone can purchase a domain name, set up a Web host or lease hosting, and publish anything they want with nobody able to edit it or mark it as suspect or inaccurate. Between word-of-mouth, books printed by whoever the hell wants to, Web sites with no validating authority, and forums where inaccurate posts aren't edited by moderators or community and are often supported by a circle jerk of clueless idiots, where do you expect to get any authoritative information?
Wikipedia has the public access problem in a different scale: anyone can post anything on the Internet or in books or private magazines without contradiction; but, on Wikipedia, you get only as much contradiction as attention, amplified inverse to plausibility. That is to say: if what you post is not obviously wrong and not on a high-traffic article, it will probably fall through; if what you post is ridiculous or is on a high-traffic article, someone will notice the inaccuracy.