Do you ever think about particular publishers when you're looking for a book? If you're like the vast majority of the book buying public this rarely if ever crosses your mind. You don't care who the publisher is. You might be interested in the author or maybe the series but publisher names are a lot like record labels; they aren't the primary (or even secondary!) brand on the product.
There's a great summary of this over on The Huffington Post. One might argue that some of those publisher names/logos on the spine help lend credibility to the book. I'm not sure I'd even go that far. Is a book really more valuable, enjoyable or useful just because it comes from one of the big-name publishers? I can't say there's a direct correlation, or certainly not all of the time.
In reality, the author, series or other element of the book is the brand that's being built and sold. That makes it harder for some publishers to create a meaningful online presence, but then again, even those publishers can be successful by leveraging their author/series/other brands online. Wiley is a great example. Although the name is well-known in the industry, and even by a large number of current/former students, the real brands (and online draws) are For Dummies, Frommer's, etc.
So which model is better: A publisher that is itself a household brand name or a publisher that manages a number of author/series/other brands? It depends. It depends on the reach of each of those brands, whether the publisher really owns those brands and whether that ownership is outright or through a licensing deal. Another factor is the extensibility and expected life of each brand. Is the brand already maxed out and there are no additional ways to leverage and monetize it? Is the brand at the end of its expected lifecycle?
So although most publishers themselves aren't brand names in the marketplace, they're still very much involved in brand management with their authors, series and publishing partners.