I think >>97 is on base, with one gigantic, glaring difference.
When a paper is submitted to a physics journal, it's reviewed exclusively by actual physicists. That's not J. Random internet nerd, it's a person who's been active in the field for decades, and who is actively involved in researching physics themselves. They generally have at least a master's degree in the subject, and many have ph.D degrees. The standars assumption of peer review is that by having physicists read research articles about physics, they're much more likely to catch an error in the paper than ... well nonpeers, who know nothing about physics. They'll have a "bullshit detector" based on an understanding of physics, so that if a proposal violates laws of physics or requires a constant to have a value other than its empirical value, the peers reading it can send it back for further testing/revision.
When an article gets submitted to Wikipedia, all bets are off. The article is edited by anybody, reguardless of the person's actual knowledge of the field. If you dropped out of high school and formed your entire view of physics from Star Trek, that doesn't stop you from "correcting" the article on general relitivity written by Proffessor Smith, particle physicist from MIT.
The problem is obvious, the WPdia system doesn't look at credentials, and not everyone's knowledge about every subject is equal. That's going to lead to errors, especially in subjects where the actual truth runs contrary to common sense, or fields that require a lot of study to understand. I'm not a physicist, and therefore I don't understand quantum mechanics well enough to be explaining the subject, let alone writing an article that nieve High Schoolers will turn to when they have to write a report on Quantum Mechanics.
That's what makes WPdia useless for serious research (school papers and the like). Basicly, with WPdia, you get concepts explained to you by people who don't unserstand the subject much better than you do, and in fact probably are either confused or mislead into believing some things are true that aren't.
Britannica may not be much better, but at least Britannica has editors who are educated on the topics they write about. Chances are good that the article on Evolution, for example, was writteen by a person with at least a BS in Biology.
Credentials and expertise don't seem as valued anymore, but really I'd still rather fly in a plane built by engineers, not one built by anyone who happened into the hanger.