Believe me, I'm not knocking Martin, or dismissing your thought. I think Martin has ended up with a world that we do fill in a lot of details ourselves, making it very rich. I also think his exceptional characterization gives us some ability to make determinations about culture and peoples. So we do find ourselves with a feeling of a fairly well realized world.
Some authors just 'get there' and others really seem to work at it. Worse yet are those that mistake world building for story telling!