Me.

Honestly, I feel ignorance plays a big part of it. It's already been said, but Nintendo has a huge collection of IPs that cover a broad collection of genres and experiences, so to lump them all together based on any of those criteria really is illogical. Even looking through this thread, most of the posters defending the qualifier don't seem to have a favorable view or an extensive amount of experience with Nintendo titles, so it seems to me that a lot of them might simply be stuck in the "Nintendo = Mario/Platformer/Mini-game" mentality. Of course, Nintendo could do a lot more help people break out of that mentality, which they seem to making headway on with several of their new RPG titles and a few IPs, but past that, I honestly can't see how anyone can play Xenoblade Chronicles or Fire Emblem Awakening and lump all their 1st party games together as "short and sweet".

Someone mentioned indie games earlier, and I think that's the best comparison honestly. It's basically a way to dismiss a wide selection a titles for completely abritrary reasons to rationalize avoidance of said games.

I think the term "Nintendo Games" has different meanings for different people. For those who were part of the PlayStation generation tend to look down on NIntendo's games as kiddy and immature. They look at them in terms of style rather than substance. Or they assume that the substance is lacking because the style isn't to their liking. The more educated gamers who use the term tend to focus more on what many Nintendo games have in common. This usually refers to the emphasis of gameplay over production values, even with games like Zelda and Metroid Prime, the unique cast of cartoony and quirky characters, and Nintendo's marketing towards the younger gamers. Not every Nintendo game fits this mold perfectly, but Nintendo's games do tend to stand out in both a positive and negative way depending on who you are.

I agree that such a statement is equally feeble, though it's not one I see often. People who dislike "most" third-party games are more common, though such a phrase is so vague it's completely useless, as almost all total shovelware falls under the umbrella of third-party games, so it's understandable for most of them to be unappealing to many gamers.

The gist of what I'm hearing in this thread is that such statements come from ill-informed or uninformed gamers. I think everyone on this site ought to know better than to say things like, but clearly some do not.

And this is why I'm a Nintendo gamer.  Ha!  To be fair, I once loved the PS brand as well.  The high sticker price on the PS3 and their similarity to the 360 last gen pushed me away.  LBP seemed nice, but not enough to satisfy my craving for Jak and Daxter and Ico (Last Guardian, where art thou?).  Nintendo games have polish and can be "cartoony."  They also can be really freaking weird, in a Japanese kind of way such as Chibi Robo.   

No, just no! It would be like saying I enjoy dreamworls or Pixar movies or like saying I enjoy Steven Speilberg movies. This is a logical statements. Book publishers are not video game developers, therefore this whole forum is rubbish. Nintendo assess every game to a certain standard. It's completely different. 

All third party games are games not created by the system makers and therefore won't have a "specific use in mind that the 1st party has. Therefore, although Nintendo games are clearly defined, 3rd party games are harder to define and categorize, but they can still be categorized. It's not really anyone's place to tell someone what they can't dislike. I might like all cars that aren't Ford. I might dislike all cars that are not ford. It would be weird to tell me I'm not allowed.

It's never used in that way. It's only ever used as a catch all for games made by Nintendo. Nintendo published Bayo2, but Bayo 2 is NOT one of the games people are thinking about when they say "Nintendo consoles are great if you like Nintendo games".

So your analogy to Random House is way off base. The analogy is "I like almost all of the books written by [insert name of author]". Now doesn't that actually make sense? If you've read a few books from one author and liked them all then you will be well disposed to buying that author's work in future. Alternatively if you've read one book from an author and thought it was not very good then you won't be trying them again any time soon.

Same would apply with Nintendo, you like the games they make, you are likely to keep buying their console. You don't particularly like the games Nintendo makes, more than likely the games you do like will be available, and run better, on a different platform.

Hence the main reason to get a Nintendo console is to play the games Nintendo makes. Hence 3rd party games sell quite poorly compared to Nintendo made games. Contrast to MS and Sony consoles where 3rd party games are typically the best selling games.

Nintendo may produce a variety of genres, ranging from cartoon platformers like Mario 3D World to epic JRPGs in Xenoblade and its sequel and dark sci-fi in Metroid, but their design philosophy is generally consistent across their library; an almost obsessive level of polish, accessibility to both beginner and veteran gamers, tight controls, and elegant world design.

Nintendo = polish (no not the nationality) + little details that are completely irrelevant but still there because they love making games.

Another thing that comes to mind is this:
Platinum Games works with publisher Nintendo
= Bayonetta 2

Platinum Games works with publisher Activision
= Legend of Korra

One gives you enough money most importantly enough time the other one does not.