It was a very interesting discussion. I like NPR, however, the discussion was very teleological. It is easy to deconstruct something tried and true after it has been put together and used for almost 75 years and find symbolism or reasons for its being the way it is.
English professors and musicologists do it all the time. Very often, when asked about symbolism, authors have stated that their novel is "just a story" and people attach meaning to them. Composers write what they write [if they are good at it] because they are brilliant and know what sounds good, so when you deconstruct it, you say it was a stroke of genius, which it may well be but my point is they don't say to themselves, "I have to finish on the ethereal high note of Oz that I used as the second note in the song," while they are writing it. As Fast/Forward said, "I feel though that things just fell into place because of song writing experience."
While Over the Rainbow is an undisputed classic, I doubt the composer thought about the notes in the same manner as the people in the interview discussing the song as he was writing it.
Yes, I know, I'm a prosaic, cynical soul. Oh, sorry, there really isn't a soul.