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I want to point out that there are costs associated with high-quality publishing that I don't think have been mentioned thus far. Peer reviewers do their vital work for free, but someone has to administer the process -- track the submissions to a journal, get the articles out to reviewers, remind reviewers to submit reviews, correspond with authors through revision/acceptance/rejection. The scientist (usually "editor-in-chief" of "chief editor" of the journal) who does this on behalf of a for-profit publisher is normally paid; in other cases, the scientist-editor must hire an assistant to help, and someone must pay the assistant. If the journal is pub'ed by, say, a non-profit academic society, the society staff may do this work, and that staff need to be paid.
Also: copy editing. It has value, when done right. Styling (making all headings look alike, making elements like equations look right and alike, etc.): Reasonable people may disagree on the value of this; I think it helps. "Production": If you have copy editing and styling, you must have checks and back-and-forth between author and proofer. Printing: Until all journals go to all-electronic, someone's gotta pay to produce the print copies. Mailing: As long as there is print. . . Copyright enforcement. Etc.
Now, these services need not be done by for-profit publishing companies. Academic societies do some of it and tend to charge much less for their journals -- which are often of equally high quality or even much better quality than those produced by the for-profits -- than the for-profits. I just hope that the employees who do this work are paid decently. (Non-profits are known for their long hours and low pay.)
Any useful discussion of the future of the academic journal must account for these realities. If/when publishers are out of the mix, some other sorts of entities will need to step up.