I heard it's a populist/farmer anomoly. Takes place in Kansas, breadbasket of the country. Farmers/agrarians were the scarecrow- no brains, but well-intentioned souls. Tin man was rustbelt mechanical revolution- tired, with no heart. Cowardly lion was.... don't remember. The wizard has to represent big government- let's go see him. He has all the an$wer$, but pay no attention to the reality behind the curtain.

I'm sure the Dark Side of the Moon parallel is much more entertaining, though.