We're still slowly getting more droplets of details on the Wii U, including its backwards compatibility options. It will support Wii games and can sync with the Wii remotes, but that support doesn't include upscaling. Giant Bomb reports that Nintendo head of public relations Mark Franklin confirmed it yesterday.
Franklin also confirmed that the Wii U won't play GameCube games. This seemed likely, since we'd seen no indication that the system even has the necessary controller ports, but it's nice to know for sure.