A friend recently published a Kindle Single, about 16,000 words. It's done quite well, largely because of three factors: Amazon marketing, the popularity of the subject matter, and timely external events tied to the subject matter. The piece is currently in the top 120 of the Kindle store.

I'm certain that Amazon marketing has played a significant role in the initial success of this piece. On the other hand, I proofread the final draft that the author had before approving the piece for publication. The Amazon/Kindle person he had been working with as a proofreader supposedly had 25 years experience proofreading at the NY Times. I probably found 100–200 errors, not the "I would do it like this: kind, but the "this is wrong" kind.

When I spoke to my friend/author later on, he said that the proofreader is simply overwhelmed with work. I can't remember how much she once described to him she'd have to do in short order, but it was a ridiculous amount of work.

So while there is a value add to a middle man like Amazon, I can see how there are shortcomings to what they offer since the grunt-work side of publishing isn’t their focus, even if they do a bit of it. That’s not to suggest the long-standing publishers are better, just that there are shortcomings to what each style of publisher offers, and it may be difficult for a new author to learn the shortcomings before it’s too late.