Quality comes from the authors and the volunteers who peer review submissions, not from copyright
Plagiarism, or detection of (academic) plagiarism has very little to do with copyright. Academics has it own set of instruments to prove that somebody lifted an idea or result with out attribution and to deal with said situation, and they all do not need any copyright rule.
This is true. But that does not mean that the publisher provides minimal value; it's worth remembering that Knuth lobbied hard to get the Journal of Algorithms moved from Elsevier to the ACM (where it became TALG) due to issues of copyright and pricing.
The ACM (and IEEE) are miles above the commercial publishers in this regard.
Plagiarism, or detection of (academic) plagiarism has very little to do with copyright.
The ACM says otherwise, and they are the ones who are actually pursuing cases. I tend to take their word for it.
Aside from review and editing, what else is really needed these days? Just throw it up on a website, make sure it gets indexed, and that's all that is really needed in the Internet age. For things like plagiarism, that really easy to detect if the source and copy are both online.
I know from my experience though, that many in academia would not publish papers without a journal because their contracts with the university either forbid such action or part of their contract explicit state they MUST be published by a respected publisher.
The problem isn't that Wikipedia is free. The problem is that Wikipedia is, by definition, a secondary(where it links to a primary source) or tertiary source(where it links to another link that links to the primary source). If you're doing the proper research, you should be using primary sources as much as possible. That means you should be directly citing the paper that Wikipedia is using, not Wikipedia itself.