I'd bet your average book consumer, with rows and rows of beautiful, trendy, or important books on his shelves, has read maybe 10% of those tomes. If that. 10% is probably a generous figure. Even true bibliophiles have read maybe 25-50% of their books.

There is a long and well-known phenomenon in the publishing world, which I'll call "trophy collecting." It's the process by which someone buys and conspicuously displays popular or well-regarded books on his shelves, mostly for the social esteem of being seen to have them. This is, more or less, how most literary fiction and wonky nonfiction gets sold.