This may be a generational thing. It's surprising the difference that makes. Back in the 90's, when I was teaching Media Studies, I played my students some tapes of 'The Goon Show', 'The Navy Lark' and 'Round the Horne', all popular radio comedies in my youth. The kids couldn't understand them! Without visual input, they were completely adrift. Also, they were utterly unaccustomed to sitting quietly and listening to something. To them, radio was music as background noise to whatever else you were doing. I can easily imagine that many younger folk, having seen the films, would find the books easier to access now they 'know what the characters look like'. Unlike us older folk who had read the books, had our own mental images, and may have found the film versions jarring. People seem to have lost the capacity to form their own images of characters.