The thing is that, in today's core gaming, graphics (and hardware in general) are very important as they clearly affect the dynamic of the experience.
When you run through the forests in Witcher 2 you really feel like you are IN the forest. The immersion is amazing. Travelling and exploring in such amazing environments is an absolutely incredible experience. The game would still be good without them, but the experience would never be quite the same. On the other hand, the forest in Skyward Sword is boring, there's no sense of atmosphere and immersion which, in the case of an Action/Adventure, can be a really bad thing.
Back in 2002, if Nintendo had offered just a beefed up N64 instead of the GameCube, a game like Metroid Prime would never be quite the same, amazing, experience that it was. It could still be a good game as far as gameplay goes, but the overall experience would never be the same.
Zelda and Metroid are two titles that need the hardware, it's a real shame to hold them back.