I must ask you again what do you understand for "niche". There is a reason why Sony and Microsoft don't even bother to compete against Nintendo, and it's because they are just too big to be fought. You are talking about the company who practically invented and still owns gaming when it comes to the mainstream in the american continent. The fact that the PS2 might have sold more doesn't mean that Nintendo isn't the most powerful gaming company. Again, other companies just prefer to ignore them and don't even dream of making a portable system of their own, because that's like having a death wish. I wonder if Nintendo is too kid friendly for you and that's why you look down on them.
PS2? Come on. This isn't the early 2000s. This is 2016, a wicked era of post-modernism, and the console market is in dire straits. Not the PS4 -it has the most loyal following, and it's the winner of the generation by a pinch.
As you might know, Nintendo is introducing its next console, codenamed NX, March 2017. The other companies have also talked of replacing current platforms. Should Nintendo get the same result as with the Wii U (that is, NOT clearly improving sales), it could very well release no more hardware and become a third party, much like Sega.
By the way, Nintendo following is estimated by some at 13 million. The current generation damaged Nintendo's finances greatly, but they held up because of the awesome earnings of original Wii (that was, you know, aimed at the general public more than to gamers). All of this is info from fresh sources, and I doubt they are in the wrong.