[xerula]

Editorial support and guidance is traditionally provided by the literary agent, so there is another professional layer between the writer and the market to consider. Big publishers maintain links with literary agencies based on the agencies' reputation for signing and nurturing talent and delivering ready-to-publish manuscripts that will sell. This arrangement persists at least in the world of commercial and literary fiction.

[grey-area]

I think that might depend on the territory/genre/author in question - in my experience many publishers provide the sole editorial input, sometimes going as far as deciding on the content themselves, with the author employed to write to hire, but this varies widely depending on the subject matter, the publisher, the popularity of the author, and probably the country as well, and obviously doesn't apply to fiction.