Those games are natively standard definition and the Wii U doesn't re-render them for HD. You're playing them in 720/1080p on the WiiU but the console's not doing anything special for it, just upscaling the picture.
Wii games on my tv look amazing. Almost as if they're in HD quality, I have it in 16:9 aspect ratio as well.
My tv must have a good upscaler in it or something. It's an older tv as well. It's a 46" Samsung Plasma from about 2007 or so. My NES, SNES and N64 games (playing on the original consoles) all look good on the tv as well.
I wish wii u does what dolphin does and auto adjust the pixels
I don't get why Nintendo didn't, it's not like the Wii U can't handle Wii games at 1080p in its sleep.
Because the Wii U is not emulating the Wii mode. There's hardware in the Wii U that operates at the Wii-level. That's how they are capable of maintaining a 100% backwards compatibility rate. But, because they are utilizing this kind of hardware, they are also restricted to what it can do, like 480p native rendering.
http://lazerlight.x10.mx/ - Lazer Light Studios - Home of the MM2 PTC project