Because Lord help someone tries to make games accessible!
They knock the Wii's graphical capabilities, mostly. Not only is that kind of pathetic, it also goes against the Wii's marketing campaign. Think about it: what is the percentage of people who own HD televisions? Very low, no doubt. I certainly don't own one. If Nintendo is aiming for the Wii to be bought by everyone, why would they force people to buy a 3000 dollar television just to get the most out of the system? That's rather counter-intuitive.
Another thing they knock is the controller. The controller is fine. Great, even. What people don't seem to get is you don't need to swing it around to much. A simple flick will suffice. But then people complain, and we get the Wii Motion+. Now they're going to complain more because it is now required to perform to action to get results.
The only thing I do agree with the haters on is the wi-fi: Friend Codes are a terrible idea. I get that Nintendo wanted to protect the children from predators. That's all fine and good. But if you really wanted to do that, why would you give us an Internet browser?! That makes no sense! You can still access social networking sites and porn, so the protection fails! Bottom line: get rid of the Friend Codes, Nintendo.