It has black bars because the Wii's output includes them. We didn't see those before because most TV's have overscan at 480p. The safe area is 640x456It isn't a great scaler, it's just a line doubler. What was once 640x480 (native Wii NTSC resolution) becomes 1280x960. That's why there are black bars, because 960p doesn't fill up a full 1080p.
out of 672x480. That's exactly how the Wii's video output looks on a scaler at 1080p.