Doesn't everyone buy a respective console, primarily, for its exclusives?

Not really. Most people buy a console to have access to the widest variety of games/genres first and foremost. Exclusives are then used to tip the scales one way or another. 

Systems that relied primarily or almost exclusively on 1st/2nd party games: N64, GameCube, Sega Saturn, Sega Master System, Sega Dreamcast, Wii, Wii U, Turbo Grafx 16. 

Generally speaking of that bunch, the Wii (fuelled by the motion gaming craze) is the only one to have achieved a really high level of success and the only one that wasn't routed by a competing console that had a higher variety of games. 

To be honest in the 80s and early to mid-90s that's what Nintendo was actually known for ... you HAD to buy Nintendo because you didn't want to get stuck with a Sega Master System that had some admittedly cool Sega games but literally nothing else. The NES had everything ... hockey, basketball, football, racing, action, shooters, RPGs, in addition to Nintendo's games. 

On my NES I played Megaman 2 and 3 and Contra and Super C and Metal Gear and Blades of Steel as much as any Nintendo game outside of maybe Super Mario Bros. 3. And on my Super NES, I easily poured more hours into Street Fighter II than any Nintendo game. Don't get me wrong I always loved Nintendo's games too, but it was never a "either or" choice before the N64. 

Not sure why but I laughed at the party people line, now back to partying.

Yes I only bought it for Nintendo games. I don't need any other console though, I will get a nice PC this year, so no more third party games on those filthy peasant consoles for me!

Specially because that means that Nintendo lost the entire market share that want to play GTA, CoD, BF and company.

Well, yes, mainly, although my collection has far more third party games than first party games. But I did buy my 3DS and Wii U primarily for Zelda, Mario, Metroid, etc.

I will say this though. In my opinion Nintendo's first and second party output is so consistently great that, if forced to choose a single manufacturer going forward, I would pick Nintendo, despite the dearth of third-party blockbusters.

The Wii U doesn't have that many first party games on it either. It must suck buying a console for only exclusives and then find out you have to wait 5 months in between releases.

Wii U really isn't any different from any of Nintendo's consoles the last 15-16 years, they all had multiple droughts. They just don't have the gimmick of motion gaming to bail them out this time. 

Without that it's just continuing the pretty steady decline they were on from SNES to N64 to GameCube. 

The last Nintendo console that didn't have frequent droughts was the Super NES. 

I noticed people just repeating that without tablet controller price could be $199.99.

That's not true, production costs of tablet controller is about $60-70, and production costs of Wii U Pro controller that could come instead of tablet controller is $15-20, that means the price would be $249 without tablet controller, but now you will have costs of rebranding, Wii U only gamepad tablet games adjustment, production contracts for tablet controller, negative impact...and so on.

In best case price would be $249 without tablet controller, and console will be lost only unique thing (except games) over competition for max $50 lower price, thats why Nintendo is not rejects Wii U tablet controller, and instead they will focus on tablet controller.

This, today 199$ is nothing.

so, would anyone care to admit, then, that the success of the Wii was a "fad" (I don't care if the sales sustained for a while) insofar as a lot more people bought it for the motion controls, and not so much the Nintendo games themselves? "Capturing lightning in a bottle" as some would say, regarding the runaway success of motion controls.

If it was bought for the Nintendo games, it would have sold like the WiiU now, and the GC and N64 before it, because people bought those systems for the Nintendo games as well (considering their respective 3rd party support was pretty poor as well, compared to the competition). And Mario, Zelda, Mario Kart, etc. haven't blown up between generations like Modern Warfare blew up the CoD franchise from a 2M seller to a 25M+ seller, for example, so I don't think you can say a game like Mario Galaxy helped the Wii sell 100M