A great deal of Nintendo's games are or have been tech demos, the Mario franchise in particular. But you've also got stuff like the Pikmin games which are literally about showing off the system's ability to portray environments and generate *this many* active elements in the field at any given time. Essentially anything developed in-house by Nintendo is their attempt at showing other developers what can be done and how to do it.
Their second parties are the ones that actually use Nintendo IP to explore the limitations or uses of their systems (this used to be Rare's job, as they always pushed the limits with their games. HAL as well, pushing the limits with the early Kirby games. These days it seems like things fall on Retro and Sora [I know they aren't technically second party but really] to evolve the properties beyond tech-demo status). This is also why Nintendo has so much variety in their IP... they don't just create a game to continue the franchise. F-Zero was showing off Mode 7 and during the N64 and GCN eras was used to show off playing speed (BLAST PROCESSING), the Mario games have always been about showing off physics all the way back to when he was literally called Jumpman because Donkey Kong had actually gravity, Zelda and Metroid (and in Metroid's case it was also about exploring vertical movement) were about demonstrating what could be done with the HUGE ENVIRONMENTS Nintendo's consoles could generate, Star Fox was about the Super FX Chip (and so was Yoshi's Island, though to a lesser extent) and Star Fox 64 was a similar idea, since the N64 was basically an evolved and integrated Super FX (in concept. I don't know about the tech). When they started making Star Fox games to continue the franchise is when it started to "fall apart" (according to some people... I personally find the post-64 games to be better, but what do I know?).
Basically Nintendo has always worked well with the "Just showing off and learning what we can do" mindset.
Edit: I don't want this to sound like I'm trying to argue with Kosheh; I'm just elaborating/exploring the subject.
Their second parties are the ones that actually use Nintendo IP to explore the limitations or uses of their systems (this used to be Rare's job, as they always pushed the limits with their games. HAL as well, pushing the limits with the early Kirby games. These days it seems like things fall on Retro and Sora [I know they aren't technically second party but really] to evolve the properties beyond tech-demo status). This is also why Nintendo has so much variety in their IP... they don't just create a game to continue the franchise. F-Zero was showing off Mode 7 and during the N64 and GCN eras was used to show off playing speed (BLAST PROCESSING), the Mario games have always been about showing off physics all the way back to when he was literally called Jumpman because Donkey Kong had actually gravity, Zelda and Metroid (and in Metroid's case it was also about exploring vertical movement) were about demonstrating what could be done with the HUGE ENVIRONMENTS Nintendo's consoles could generate, Star Fox was about the Super FX Chip (and so was Yoshi's Island, though to a lesser extent) and Star Fox 64 was a similar idea, since the N64 was basically an evolved and integrated Super FX (in concept. I don't know about the tech). When they started making Star Fox games to continue the franchise is when it started to "fall apart" (according to some people... I personally find the post-64 games to be better, but what do I know?).
Basically Nintendo has always worked well with the "Just showing off and learning what we can do" mindset.
Edit: I don't want this to sound like I'm trying to argue with Kosheh; I'm just elaborating/exploring the subject.