Klockan3 said:
So I would guess that it is mostly very minor stuff that would never get published at any of the larger journals.
It's very field dependent. In finance and economics, getting something published is an extremely difficult process as the peer review panels consider themselves gatekeepers. Physics, mathematics, and astronomy journals peer reviewers usually have the attitude that they aren't gatekeepers, and their job is to get rid of the really silly stuff, provide a very minimal level of quality control, but otherwise let the community decide what papers are good and what ones aren't. I think that it's been mentioned that about 70% of the papers that get submitted to Astrophysical Journal eventually get published. By contrast, Nature and Science, whose policy is to only publish the cream of the crop papers, have something like a 5% publication rate.
I think the reason that the publication rates are high are:
1) there's often no reason that a peer review panel can give not to publish. A lot of papers in astronomy are basically, I pointed my telescope at this object, got these results, and here they are. If you are a peer reviewer, and the authors aren't obvious idiots, then what can you say? If you have a mathematician that claims to have proven a theorem, your only real excuse for not-publishing is that there is a mistake in the proof.
2) the major journals are under the control of the professional societies, so there is no real financial reason not to publish huge journals, and
3) finally, funding. The gate keeping in physics/astronomy happens at the grant proposal level. If you have a scientist that got a grant, did the work, and the results were decent, and the journals refuse to publish, they are going to be looking at some very serious conflicts with the NSF. Also a lot of the programs that finance undergraduate research come from NSF, and the National Science Foundation wants to see undergraduates publish.
Personally I like the physics/astronomy system in which the journals will basically publish everything that isn't totally insane. The problem with the economics/finance system is that you have terrible, terrible inbreeding.