For those who don't get why the whole business of the 1939 film turning the story into a dream-fantasy gets my privates in such a knot, I refer you to Tolkien's essay, "On Fairy Stories." But to summarize, dream fantasy is an entirely different genre, one in which the stakes are basically zero. It works very well as a vehicle for absurdist political satire (which is why Lewis Carroll's "Alice" books work so well), but anywhere else, you end up with the 9th Season of Dallas, leaving your audience with feelings of betrayal.
The "ruby slippers" business was just an annoyance. And not nearly as big an annoyance as MGM's tendency to act as if they owned anything other than the liberties they took with the story, or the shocking number of people who act as if the movie were the canon source and the book was an adaptation, evidently not realizing that the book predated the movie by decades.