It is already integrated, since the SB850. But like with any other integrated network, you need an external PHY chip to be able to use it. However, because AMD bought the IP from broadcom, only an expensive broadcom PHY is working, hence an additional, dedicated REALTEK PCIe Gb-chip is less expensive.

Furthermore, there are the volume-contracts with Realtek or intel. The more you order, the better the price, thus you try to only have *one* PCIe-chip for all your Intel/AMD mainboards to cut down costs.

Therefore next to no desktop-board is using the integrated MAC on AMD chipsets. I have not checked the server boards.

P.S: You cannot integrated the PHY, that is some analoge device which cannot be designed in smaller processes below 65/40nm or so. Hence, you always need a PHY, hence you have to waste one PCIe lane anyways, and that lane can also be used for a fully integrated Gb-chip. Not much difference.

interesting, but I'm sure chipsets are made on much larger processes than CPUs, most are 40nm