It might be somewhat less true in spec fic, where many readers attend conventions at which there are editors from various publishers. But in general, most readers don't pay any attention to the publisher, only to the writer. The writer is, in effect, the brand, and the publisher's name is just a word and a logo on the title page. Booksellers (wholesale and retail) have always paid attention to publishers' names, but not readers. One interesting tidbit of info in the whole Amazon-Macmillan kerfuffle was that Macmillan saw Amazon as a customer. This came as something of a shock to readers who thought they were the customers. They were also mad at Macmillan without really knowing what Macmillan was, i.e., what imprints were under the Macmillan corporate structure,
With many products, the brand identity is keyed to the manufacturer's name. Look at Apple for a prime example of brand identity. It's not just an iPod, it's an Apple iPod. By stressing its products' quality and maintaining a distinct design, Apple has built some fabulous brand loyalty (Apple also has its detractors, but at least those folks know what they're against).
Publishers can't really do that because every author's work creates its own following, and authors can and do change publishers. Publishers can try to impose a level of "quality," but the fact is that just because a book is well written doesn't mean everyone will like it. Some genre publishers have carved out niches by publishing only certain kinds of books. Baen is an excellent example. Until recently, they published mostly military science fiction, giving fans of that subgenre a reliable place to go for that kind of book. But it's difficult to grow revenue with that kind of strategy, as filling a niche means you can only be as big a business as that niche.
So, here we are, poised on the brink of the digital revolution. It won't happen overnight, but over the next ten years, publishing will change radically, as new technology provides new, more convenient ways to read and experience books. I may write spec fic, but I can't pretend to predict how things will look in ten years. But I do think that one thing publishers will need to do to survive is to establish themselves as a brand with their readers.
A lot of digital enthusiasts predict that publishers will be less relevant because authors can branch out and publish digitally on their own. I don't actually see that happening any time soon for several reasons. First and foremost, authors don't want to deal with the business side, they want to write books. Second, print is still much bigger than digital and will remain so for quite a while. Third, most successful writers know the value of good editing.
But here's a little quiz to prove my point. Without looking on Google or Amazon, which publishers can you name for these books? Leave a comment and tell me!
DEAD IN THE FAMILY (a Sookie Stackhouse book), by Charlaine Harris
UNDER THE DOME, by Stephen King
CHANGES (a Dresden Files book), by Jim Butcher
BLACKOUT, by Connie Willis
OATH OF FEALTY, by Elizabeth Moon