Hub cones wear much faster than the cups do for two reasons: there is less surface area to distribute the load, and bearing pressure is concentrated on the small portion of the cone facing down toward the road. Unlike the cups, cones do not rotate when the bike is in motion. If you don't "rotate" your cones so different sections are exposed to the highest bearing pressure, the cones will tend to pit sooner. The cones get "rotated" every time you remove and reinstall the wheel (This assumes you are not like one of my old customers who insisted on installing his wheels so the groove in the axle always faced forward). Recreationally ridden bikes with nutted axles and heavy duty tires are especially susceptible to cone wear, because their wheels are seldom removed from the frame.
Kevin Ko
Eugene, OR