Wii U's sales are not the result of any kind of long term trend, they are the result of the incredibly poor handling of the Wii U itself, individually.

The Wii was a fluke

I expected some drop but not to this extent. I don't think this is part of any long-term trend either. Wii U was just poorly marketed from the start. Nintendo attempted to placate core gamers that seemingly moved away from the Wii in the later half of last gen and marketed it with core games in mind (e.g. Zombie U, Bayonetta 2, third party links). At the same time they tried to keep the casual market with the tablet-style controller, but neither strategy seems to have worked.

The controller is a solution looking for a problem resulting in Nintendo struggling to get a coherent marketing message to consumers.

You are right. I read it so often that I know think the same way. I should get this out of my head! Nintendomination!

The reason Wii U is doing poorly compared to the GC is not due to this downward "trend", rather due to Nintendo's incompetence with launching the thing.

I was expecting Wii U to perform bad when they announced, the Gamepad seemed a very bad ideia to me. But after playing the console for the first time, I really enjoyed it overall and it has many good games already, so I think it will sell better than NGC (and maybe N64) if Nintendo advertise it properly from now on. In my opinion, with MK8 alone it can already surpass 20mi, because it is the game that will make more people play the console and see that its concept is not bad at all.

The "Wii U Pitch"-commercial inspired me:

https://www.youtube.com/watch?v=bso27e3Inzc

Wii U's sales are worst even than Gamecube's. Gamecube was a great console and deserved more sales but Wii U is getting what deserves, let's see what they learn about this.

Not true.

Fluke implies luck.

Wii was not lucky; it was a premeditated, calculated success.

Yes. It was a one time thing and won't happen again.