As to separating books by publisher, who but a hack or someone personally friends with someone at the publisher would even think of such a thing?
I don't know. Just the other day, in a thread at io9, people were discussing how they associated different publishers and imprints with different flavors of SF. How you generally expected one kind of book from, say, Baen Books and another from Nightshade or Del Rey. And Lord knows I've contended with bookstores that insisted on shelving all Tor books in the SF/Fantasy section even when they were actually mysteries or historical romances!
True, I suspect the average reader ignores the colophon on the spine, and couldn't care less who puts out what, but my impression is that the more knowledgeable sf and fantasy connoisseurs do
play attention to "brand names" as it were.
(And I prefer "modern-day pulp writer" to "hack," btw.)