Note.  In my digging, it was Dover, Von Nostrand Reinhold, and Henry Abrams that seemed the most prolific mid-20th century publishers in the artbooks, sourcebooks, historical collections realm.  

And where are they now?

They're obviously still around, but their "dominance" has been supplanted by more modern entities like Phaidon, Rizzoli, Powerhouse, McSweeney... and many others.  There's more visual arts print material now than ever before.

Wow! Really?! I would never have known that industry is booming if you hadn't said so. 

Hopefully my statement wasn't a naive one. But as far as I can tell, there's more visual content floating in the world now than at any other time. Even if "print" industry is "dying," that sentiment has more to do with large, old newspaper press media and their shit secondary glossy mags. There is actually a burgeoning and thriving independent publishing industry - niche portfolios of titles, curated stable of artists/designers/editors/writers/stylists/producers.  The same trend has been forecast (and exemplified) in, for example: VC/investment world, Film, Vinyl Record revival, and even manufacturing, with the rise of 3D printers/Rapid prototyping.

Further, in today's post-Creative Class globalized world, there are that many more Designers (of which Graphic and Industrial are the leading disciplines). More graphic/industrial/packaging designers around the world necessarily translates into projects that result in physical goods being produced.

Check this site out for example: http://www.nolayout.com/. And this is only Zines, which are even more simple to produce than perfect bound/saddle stitch book-style magazines. Blurb did have a role in helping DIY publishing along, but I bet that online bespoke book production can be done through more services/sites now.

I don't know, I'm not really an expert.  But I can't tell you how many times I've discovered a new fashion/photography/design magazine from another country - and most are better than what we have in the US.  Our aesthetic taste here sucks.

Fascinating perspective and analysis though. I believe you. 

2006: http://www.amazon.com/Left-Right-Cultural-Shift-Pictures/dp/2940373361

Wow! I see what you mean.