I've worked on great hubs (Dura Ace and Chorus) and really low end entry level hubs (Sansins, low end Maillard, a couple of Wal-Mart bikes, etc.) and even the cheapest can feel smooth if well greased and properly adjusted. The good ones feel super smooth and are more durable long term but nothing has to ever feel "like gravel" until the races and cones are badly pitted.