Gross margin, as I understand it, is the percentage profit on manufacturing all the combined products that Apple sells. If Apple brings in 100 dollars and gross margin is 33 percent, then it cost them 67 dollars to make it and they get 33 dollars profit on that revenue. Gross margin only has to do with the cost of making the product, like the components (the NAND/DRAM flash memory, LCD screens, optical/disk drives they are talking about). Operating margin factors in other costs related to bringing the product to market, like transport and marketing costs.
Anyone else have a different explanation or anything to add?