What Are The Essential Parts of a D&D Setting?

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Forum member Cyberzombie asked a good question earlier this year.

What are the essential elements of the most generic of D&D settings? You can, of course, dump just about anything and everything to create your own setting. But what I'm looking for here are the elements that scream D&D -- things you must have in a setting to have the D&D feel to it. Simultaneously, I'm interested in what things could be dumped without hurting the feel of D&D. What could you rip out and still have something that feels like D&D?

Since my introduction re-introduction to Dungeons & Dragons and Role-Playing Games in general was so very unorthodox, with Lonny's group from Bradley immediately being thrown into a Dark Sun campaign, I'm not sure I could best answer this question. I mean to explain that I feel there are no essential elements that cannot be removed and there is nothing that could not be added. There are going to be traditionalists that state that you couldn't possibly remove dragons as a story element, and yet on Athas, for all intents and purposes, dragons as they are commonly known do not exist. And that is just the first difference from a traditional setting.

To introduce players to the game, perhaps the more traditional and expected elements should be in place.