I created this simulated comparison image using Rock Band 3. It's not a very pretty-looking game but the point still stands. First is Wii, Second is Wii U.http://imgur.com/9DWY4,R5A0Z#0
The 480p rendering of the game is scaled up to fit an HD resolution like 720p internally with the Wii U, then sent to the TV via HDMI. This is better than what the Wii was doing by sending the signal to the TV via component, then having the TV scale it up to the TV's native resolution.