Couple of things to consider:
If Nintendo decided to not continue some of the huge franchises fans would be jumping on them for it. How many times have we heard 'Where's starfox and fzero wii?' Shoot, I've even been on the band wagon for DK since the horrible gamecube outings. I think it is the whole 'give your consumer's what they want now versus what they want 2 years from now' dilemna. The latter can at times fail. Fans always want their nintendo games plain and simple.
Nintendo's extensive history also gives them this stigma of recycling old franchises. Looking across the industry when a franchise is successful it is continued, and possibly even squeezed dry. Final fantasy(more titles than super mario with less variation in less time), sonic, resident evil, gran tourismo, ratchet and clank are all guilty of this. Nintendo has a similar model to others, they've just been around longer.
Also, how many new IP's are you looking for? Each gen has brought us a few. SNES: star fox, fzero, and kirby N64: smash bros(pretty much a new IP), pokemon GCN: Pikmin, Animal crossing, and ~geist WII: Wii___, excite(pretty much new)
As long as a couple new franchises are brought each gen I'm content. Third parties(assuming they try) will bring games and possibly new IP's aswell.
After Miyamoto is gone I think you'll see a shift.
