Part of the hate is due to misinformation as well, I can see it in the thread, the classic "WiiU has no games", which is just untrue, it actually has quite a lot of games, just people for some reason ignore them or bat them away with "Oh i don't like those".
What they really mean is "I don't like the games on it" which is valid complaint to some people but individual to each person, and different from "It has no games" which is just false, considering it has more games than the current next gen consoles (yes due to being out for longer but that doesn't stop people shouting it)
Then there's the classic "Nintendo has no accounts system", again quoted on here, which again is wrong, they do have an accounts system, all of your purchases are tied to an account, its why you can see miiverse on your phone and make purchases via the other consoles. Its just that these accounts are tied to a single console unless you contact customer support.
Now most of us will never hit this, and again its reasonable to be slightly annoyed (not to the level that some people take it mind you) that you can't log into your mates machine to play a game, but the shouting of "WiiU has no accounts system" is not accurate, but repeated none the less.
However both of these things have been shouted so often that they have gained a truthfulness in peoples eyes.
Basically its the same as cloud convincing himself hes a member of Solider

If you shout something often enough people believe its true regardless of the facts.
[EDIT]
Oh and there is also the "Should be 100$ cheaper and drop the gamepad", despite zero evidence that the gamepad actually costs 100$. Closest thing we had was a price conversion from yen to dollars on the cost ove rthere, but that was a sell to retail price, and again , quoted as fact since its taken on a truth simply because everyone quotes it. This is used as a "its overpriced because of the gamepad", then you add on the "no-one has used the gamepad well" , which ignores Nintendoland and Zombie U etc. Its just a lot of people who are ill informed shouting the same thing over and over and it taking on its own story.