I'm from NZ too. Nintendo has ALWAYS underperformed here, so I don't neccesarily agree that its casual marketing strategy is to blame. In fact, I think there is a strong case to argue that Nintendo are doing better now than they ever have in NZ.
I agree that it would be nice if hardcore games were advertised more often, but if you consider the limited attention Nintendo tends to pay the NZ market, it just makes more sense for them to focus on their most profitable titles.
Like someone suggested earlier, hardcore gamers are already well informed so its less effective to advertise to them. You even said yourself you knew that gamers games exist on the DS. You don't need an advert to remind you.
I'm sure you remember that little more than a year ago Nintendo ads were extremely rare on NZ tv. I know for a fact that Nintendo's advertising is more diverse in Australia, and I suspect the same is true of other countries. Geez, I haven't seen any DS games other than Brain Training advertised on NZ television. EVER.
Nintendo's smaller share of the NZ market is and always has been symptomatic of the poor support NZ receives from Nintendo in general, not its television marketing strategy, which actually coincided with quite a significant improvement in sales. Nintendo games simply didn't chart at all until about a year ago, and now Wii Play and Wii Fit appear frequently in the NZ top ten, which represents quite a remarkable turnaround.