Every editor wants the writer who will become the next NYT bestseller. It only makes sense that if romantic suspense is flying off bookshelves, the editor is going to be looking for romantic suspense. However, that doesn't mean if she reads a pirate historical that she thinks is superior to every manuscript she's read all year, she won't buy it. She just probably won't announce at RWA that she's looking for pirate books. Yes, market forces influence decisions.
Publishing is a business and like every other business, the bottom line is important.
Call me Pollyanna, but I still believe that risky books will always be published simply because they speak to an editor's heart. I think most of the on-line readers are savvy to the fact that the author is often unpleasantly surprised when she sees her book's cover, but not sure exactly what the author has provided to the publisher and artist to guide them. This, too, depends upon the publisher. The art department's vision is not always my vision, but I do believe everyone tries to give a book the best cover art possible. Sometimes, I don't have a vision of a cover to suggest.