Matter or mattered? We're talking about a book that was written 150 years ago. I can't think of a time when I thought, 'oh I'm going to read an entire book on astrophysics'. Like most of the population I don't have the patience or basic understanding to digest that much technical content. While I'm clearly not the target audience for such books, in today's age are academic books still just as important?the supreme demonstration of why academic books matter
I read a lot of new computing and math books and papers, because those are the fields I am educated in and I like to keep up (... and the kind of problems one gets outside of academia make me fear my brain liquefying and dribbling out of my ears). I do think academic books have much less influence now that professional demands force people to publish constantly, whether they have anything particularly interesting to say or not, and so there is a constant flood of half-baked, incomplete, and uninteresting work to plow through and if you don't work in academia you have to be very interested or very dedicated to bother.
Perhaps "are important" would be a better term for this? I do very much think that academics books matter. There are still a great deal of books on academic topics that are being published that help to break down extremely complex concepts and ideas into something that a layman can understand. The first think that comes to my mind is The Elegant Universe by Brian Greene. This book broke down String Theory into a fascinating and informative lesson into the basics of the universe.