Game cards makes sense in my opinion. They're far harder to pirate, and modern 'cartridges' (high capacity SD cards) hold a shit load of information and they're not liable toget scratched or chew up the same amount of space... Apparently they also use less power?
Economically speaking there's a couple of reasons why Nintendo is performing quite well.
1: Greater production cost and sale price parity.
Nintendo simply lose less money when bringing out a new console. This covers a WiiU style advent, but it also immediately bolsters the company's profit projections whena console/handheld takes off.
2: Proprietary access that boosts first party sales and reinforces hardware uptake.
Simply put, Nintendo are the most productive games company in the world. It also helps that their games are often incredibly well received. To put it plainly, there's only one real place to play Nintendo games... and Nintendo games are more often than not highly desirable to play.
3: A ridiculously fiscal conservative-orientated philosophy.
Nintendo is weird in that they are incredibly cautious with capital reserves. In fact, Nintendo could release a WiiU level disappointment every year until 2035 and still not go broke. With full hardware dev cost and initial shipment run cycle and everything.
4: Proprietary tech partly fueled by hardware development cycle.
Kind of the reason why Nintendo experiment with their handhelds and consoles. Also why Nintendium is in everything .... it can even say your life. Some ECG machines even run on Nintendium.