Why do forest soils have an E horizon, but prairie soils don't?

And so we have another agronomy question. It's closely related to the previous one, but I didn't feel like going back and adding this one to the last post. Over the course of this week's soils lab, I learned that (as my post title implies) prairie soils don't have E horizons, but forest soils do. As I explained before, an E horizon is a light-colored layer of soil that has had minerals, organic matter, and clay leeched out of it by rain or some other water seepage. In a forest, very little organic matter accumulates on the surface of the soil. Leaves and maybe a little undergrowth are all that are added to the soil. Most of the organic matter lives for years and years before returning to the soil. In a prairie, on the other hand, all the vegetation dies each year. A huge mass of root and shoot matter is added to the soil each year. Since such a great volume of organic matter is added annually, the dark, humus-enriched A horizon stretches all the way to the B horizon below. In a forest, the organic matter isn't replenished nearly deep enough to account for the eluvating action of the rain, and so you get a light, nutrient-deficient E horizon.