They do. I'm not sure which mega-house Bloomsbury belongs to or has a distribution deal with, since it's the British market, but I would assume they have one. The large houses -- Bertlesman which has BDD and Random House, Time Warner, Penguin, etc. have general fiction, categories imprints, children's, non-fiction -- which is where they make most of their money -- and educational operations. However, in the 1990's, with the cutbacks, a lot of them spun off or dumped their educational arms, so that market is kind of separate now from trade. But Signet, for instance, as part of Penguin, still makes a lot of their money in schools and universities for Signet Editions of classic works, and there are Norton readers and such.
For publishing, I would think the big guys would adopt a similar policy: general fiction, genre fiction, children's fiction, non-fiction, and textbooks with the latter forming the base. Particularly in the latter I can see a means for formulating short-term and strategic plans to keep the company viable in the textbook market.