I think it's simply that most of these devboards are produced by the SoC manufacturers with the idea of popularising/making it easy to develop products for their SoC. So the peripherals you get are the ones the SoC has, and traditionally most of these SoCs are aimed at the mobile space, which doesn't have SATA or ethernet or PCI (ethernet on these devboards is often USB-ethernet). As the A15-based SoCs (eg exynos5) appear I'm hoping to see more SoCs aimed less solidly at the mobile market, and with a wider mix of onboard devices.