Whenever this topic comes up, we end up discussing what publishers really do.
Every time, someone with some knowledge of how the publishing industry works turns up and explains how there is this long road between the author's draft and the book in your hands, made of editing, copy-editing, typesetting, cover design, marketing and more, and the publisher is the truck driver that sees the draft to the end of that road. That's correct.
But I've come to the conclusion that none of that is the one irreplaceable service publishers perform in the system.
All of the above can, to some extent, and for a fee, be performed just as well by independent contractors. (There are great independent editors out there, and aren't we all glad for that.)
The one important thing publishers do is: they take the loss on books that don't earn out.
Now hear me out.
I know how we, Slashdot readers, tend to think about those things. In our minds, if the book doesn't earn out (that is, it brings in less money than the publisher gave the author as an advance), then it's got to be someone's fault, right? Bad writer, bad publisher. Something.
The thing is, a successful book requires a lot of factors. Great writing doesn't suffice. The public is fickle. Yesterday, supernatural romance sold by the truckload, now it doesn't. GRRM was a great writer for decades before you even heard of him. Harry Potter didn't start hitting it big until three or four books into the series. Word of mouth matters, but only after the readership has exceeded a certain critical mass. And until then... someone has to take the loss.
Because, here's the thing. GRRM, Rowling, they're outliers. Many books -- most books, AFAIK -- don't quite earn out. Many deserve to, but don't, because that's not how the world works.
But they still got written, you still read some of them, you still loved some of them, and that only happened because someone, somewhere, was willing to pay an author to keep writing, and take the risk that the great book in their hands may not earn that money back.
And that, friends, is what publishers really do.