At any particular time, I'll be in the middle of about 4 books, and maybe another 4 articles. So nowhere near as much as you. I have to devise systems for when I'm going to read stuff, and it would get way too complicated if I tried doing 30-40 at once. Even if I could be bothered to schedule that much in, I probably wouldn't be able to follow them all.
Still, maybe it depends on what kinds of things you're reading - I only ever read quite technical philosophy; maybe if I branched out a bit to other areas, or read fiction, it would be easier to keep up with so many books*. I'm not interested in doing that, though.
* Not to say that other subjects require less thought than philosophy does. It's just that everything I read gets stored under 'philosophy' in my head, and if I was reading 30-40 books, it would all become a complete jumble. Maybe if I read other things, I'd create different mental categories, and the claims (or narratives, in the case of fiction) of various books would be more easily seperable in my memory.