I think the analogy of the airplane is accurate. That's the way encyclopedias work -- for a piece of fiction or entertainment, it doesn't matter whether the facts are exactly right, if fact sometimes you need to fudge a bit to make things work. In effect, as long as it looks like an airplane, it's probably OK.
The problem comes when you try to use the airplane. If the engineering is off, you crash. The same is true when you try to use information -- having bad information can cause lots of problems. Changing a + to a - in an equation changes everything.
That's where WPdia breaks down -- when you have to use that info to make a decision, chances are that you aren't basing it on the information that is know by experts, you're basing it on the "consensus" of what J. Random Citizen believes about the subject. While experts may be wrong on occasion, or may not no the absolute latest theory, he knows what he's talking about. He's dedicated years of his life to it -- as evidenced by his pH.D in the subject. He's had to prove over and over and over that he knows his stuff.
As to self-taught, it's possible that a self-taught expert may have a lot of knowledge about a subject, but one of the big advantages of getting the degree in the field is that you can check his credentials. As an example, it's perfectly legal and possible to purchase a Black Belt and open a Karate school. You don't need to ever have studied Karate or anything else, as long as you pay the insurance and pay for the studio, you can teach Karate. However, the students of a school like that are likely to get hurt. The only way to check to see if your Karate school is taught by someone who knows Karate is to check credentials -- Who taught him, what style did he learn, what year did he earn the Shodan rank? Then you can contact his master, and see if the sensei is who he says he is.
Same with a physicist. A self taught physicist can't be checked out because no college has checked to see if he understands physics. At least with Prof. Smith, you can find out that he got his pH.D from U of Illinois in 2005. You can check out those credentials, even find out if he was top of his class or a b- away from washing out.
That's what credentials are for. Sure I could (and actually I have) read some books about physics, particularly string theory or whatever. But since I don't have a degree in physics, you don't know.
1.) Did I actually read all the books I'm claiming?
As with the purchased Black Belt, it's perfectly reasonable to claim to have read a book even though I haven't. You have only my word on the subject.
2.) Did I really understand any of it?
It's possible that you did skim these books, but physics, chemistry, psychology, and biology, etc. are difficult subjects to grasp at times.
3.) Are the books I read even relevant to the subject?
"A Brief History of Time" is completely irrelevant when you're talking about Mechanical Engineering, Chemistry, or other more practical realms of physics. Also not a useful book when talking about a cure for cancer.
That's the problem with self-taught experts. No way to check up, all you have is their word on the subject.
When it comes to encyclopedias, WPdia for this reason falls to the level of Truthiness, not Truth. It's whatever the vast majority of people believe is true about a subject, rather than varified facts about the subject.