Some interesting points are made here, even if the movie references at the end are less than current.
Until quite recently, as, once again, British novels bear witness, educated people had a cultural common ground based on literature that they could draw upon and refer to in a reasonable expectation of being understood. Everybody who read had read Shakespeare and Alice in Wonderland. Lord Peter Wimsey could quote from either, and we knew what he was talking about. We had even read Homer, if not in the original like Lord Peter (when I went to college, the Iliad and the Odyssey were required reading in Humanities 1), and could field a reference to Achilles or the Trojan War with ease. In contrast, I remember a conversation with a fourteen-year-old cousin in 2004 or so about the movie Troy, which reduced that epic conflict from ten years to three days and took many liberties with the plot. “Have you read the book?” she asked.
Nowadays, not only have our culture’s reading habits changed dramatically, but there’s too much to read. Politics have decreased the attention in the school curriculum that was once paid to “dead white males” like Shakespeare and Lewis Carroll. This is not all bad. I would have loved to be made to study Little Women or The Help instead of Silas Marner and Giants In the Earth, the two most stultifyingly boring novels I can remember being assigned in school.
As the fact that a billion people worldwide watched the Oscars this year attests, movies occupy the space in the collective unconscious that used to belong to books. Movies provide the material by which we communicate through common points of reference. Most people know The Wizard of Oz and Gone With the Wind and The Godfather from the movies they became, rather than the books they were based on. Instead of “To be or not to be, that is the question,” “My kingdom for a horse,” “I can believe six impossible things before breakfast,” or “It was the best butter,” we all resonate with “We’re not in Kansas any more,” “Tomorrow is another day,” and “I’m gonna make him an offer he can’t refuse.” How many people nowadays know that Dorothy originally had silver shoes, not ruby slippers? Some of us have read the books. But the reason everybody knows these references with all their implications is that we’ve seen the movies.
Authors now do face a situation where they can't count on other literature as a common cultural touchstone for their readers. In a way this puts them in the position of pre-Classical writers, those from the time when written language as an artistic medium - as opposed to simply a business tool - was a new thing. Of course that was so long ago that it's effectively new territory, and difficult to trek.
Of course L. Frank Baum is a natural victim of this displacement because of his very creativity. The movie of The Wizard of Oz became the definitive version for most Americans soon after it started airing regularly on postwar TV. To the extent that elements present in the books but not the movie seem outright bizarre to young readers, the silver-not-ruby slippers. And the fact that it's the books that seem strange and not the movie is itself weird. It's the film that casts as a pigtailed little moppet a teenage singer who in most respects was older than her years, not younger.
Seriously, that look was what befit a gay icon most?