NES --->SNES (2x) --->Nintendo 64 (3x) --->GameCube (3x) --->Wii(1.5x) ---> Wii U (3x)
PlayStation One --->PlayStation2 (3x) --->PS3(3x) ---> PS4 (?)
GB ---> GBC (2x) --->GB Advance (3x) --->Nintendo DS (3x) --->Nintendo 3DS(3x)
PlaySation Portable --->PS Vita (3x)
As you can see in this pattern, the Wii is the only console that didn't have any substantial upgrade compared to all the other ones shown here, which meant that most of it's games were essentially Gamecube games with a little more detailed. Of course there were new ways to play the game and Wii hardware itself allowed for a heck of a lot more features than the Gamecube did, but we are strictly speaking about graphical capabilities here since this is all what Sony and MS fans want to hear about.
Quite the difference, right?
Even if Wii U graphics aren't as good as the other two it doesn't mean that players won't be amazed of what it would be able to do. Take a look at the screenshots above for a quick example. PSP had considerable more graphics capabilities than DS and games like God of War, Syphon Filter and Peace Walker demonstrated that, but actually seeing Pokemon the way it was shown on DS was amazing to Pokemon players because it was a great improvement over it's predecessor, so even though PSP had better looking games, it was more amazing to see the transition of Pokemon Ruby, Golden Sun, Mario & Luigi, etc. from the GBA to the DS, and since most of PSP games were transitions from PS2 games they actually looked worse or equal to their respective franchise games on the PS2.
The problem with the Wii was that Nintendo's franchises wouldn't have a drastic change of how they looked on the Gamecube, so people weren't expecting much amusement from seeing new entries from classic franchises. Granted Mario Galaxy 1 & 2 and Skyward Sword look really amazing, but Nintendo's creativity can only go so far with the limited hardware. Again, take in mind that we are only discussing graphical changes, I'm well aware of how awesome Skyward Sword motion controls are and that the Gamecube wouldn't be able to give me that experience.
Metroid Prime 2: Echoes (GameCube)
Metroid Prime 3: Corruption (Wii)
Not much of a difference in graphics.
To conclude this post, I want you to think about how absolutely incredible a new Zelda, Metroid or F-Zero would look like with Wii U's capabilities, and how different they will look from the usual Wii games. Nintendo will once again show why they are one of the most creative developers out there.
I would really like to know what you guys think about this, and if you think that there would really be a drastic difference between Wii U's and PS4's graphics capabilities that would guarantee the Wii U to be outdated. I really hope I got my point across with this post.