Many of the books I read aren't available electronically yet.
Even if they were, I probably wouldn't replace them because of the cost. Ebooks cost about the same as pbooks right now, and we have two rooms with walls covered in full bookshelves.
I am preferentially buying books as ebooks now rather than pbooks when they are available.
I really like the look and feel of a library, with all the pbooks covering the walls, though they are quite a pain to move. (We've moved twice in the last two years.) Thus I would not be highly motivated to get rid of my pbooks in any case.