I always thought that was a little odd myself. In leatherworking, you turn in leather or arctic fur for recipes. In enchanting, it's dream shards. Why not either jewels or ore for jewelcrafting recipes? I also thought it odd that while LW and enchanting use mats to buy recipes, you don't need to do so with alchemy, and inscription is like alchemy in that you learn things via creation and research. Perhaps they were trying to keep people interested in professions by changing things up somewhat, but a single standard may have been better.