There's one big advantage of using an SD card only, and this turns into a really massive advantage when you consider the target market. There is no state persi

There's one big advantage of using an SD card only, and this turns into a really massive advantage when you consider the target market. There is no state persisted on the board apart from on the SD card. I have a set of SD cards, and can switch between them at will. My Pi completely switches personality, with no internal state to confuse things. Kids can play and risk breaking things as much as they want. The restore process is simple: take the SD card to a (normal) computer, rewrite the image, and you're set to go again. On-board flash completely ruins the guarantee that replacing the SD card is all that is necessary (unless there is a hardware fault).