Nintendo has a large bag of cash and a huge fanbase that will buy any console with Mario and Zelda. Will it repeat the Wii? Probably not, but that's a tough act to follow. People predicted doom with the N64. Nintendo followed that up with the Gamecube, another failure. They still survived enough to make the biggest selling console by far. With them making money on every unit sold (something MS and Sony don't bother with), even if no one bought any games they still made piles of dough. Nintendo will sell at least enough to keep going. The casual market is huge.
Sega wasn't in good financial shape to begin with, at a time when games were difficult to sell. They lost their retail partnerships by launching console after console to compete with themselves. Sega had zero credit to ride on when they folded. Nintendo will survive.
I've bought pretty much every Nintendo console they've released (and some handhelds). The post-wii world looks pretty different from my perspective:
1) The lack of quality first party titles for the Wii is very disappointing. This is a contentious point ... but every single person I know both has a Wii and currently uses it as a paper weight. Nintendo could have had something big given the penetration of the lil Wii console. I used it for Netflix for quite a while, for instance. They really blew this one though. I believe there have been no feature enhancements for the Wii home screen since release! Netflix updated recently but the experience is very poor ... I get buffering problems all the time for instance.
2) I was stupid enough to buy the 3DS the first day. The device was pretty shitty ... gave me headaches.. literally. Plus, the price reduction followed by giving old owners shitty games in return was insulting.
Based on 1, 2, and my love for the 0.99-4.99 games on the iPad, means that I am no longer going to buy consoles from Nintendo. And I might not be alone on this one.
This right here is Nintendo's #1 competition right now, even Nintendo admits it. That may be a driving factor in the tablet controller. If parents can give their kid a basically kid-proof tablet to game on, they won't get their sticky, clumsy hands all over the expensive iPad. Combine that with games for a tailor-made gaming device (iPad is not) and buttons, and you've got a pretty nice family-friendly gaming system.
With the iPad/Android/W8 Tablet market Microsoft is adding on to the 360, you could liken it to further reinforcing the division between the systems. Nintendo for families, Microsoft for college aged through adult gamers.
Not a week goes by where I don't hear someone my age (adult) say "I'm never buying Nintendo again!" In the same timeframe, there are thousands of kids coming to the age where they really want to get into gaming. I'm 20-something, and my generation is really growing out of Nintendo. But we're having kids who are just growing into Nintendo.
My nephew is 8 years old. He had a DS and loved it. BUT, like most 8 year olds, he would lose his games, and eventually his DS.
Instead of buying him a new DS, my brother bought him an iPod Touch. Same price as a DS but the games are free or cheap. Plus, he can't lose the games, even if he loses the iPod.
Of course, the iPod does more than games. My nephew loves that he can video chat with his cool uncle as well as listen to music, and all the other things an iPod does.
You're discounting two phenomena that helped them weather the tougher times and are unlikely to repeat - Pokemon (you can't really count on another such a massive media franchise popping up) and handheld gaming dominance (iPhone and Android killed this market for standalone devices).
Have they really killed it? There's obviously more casual gamers carrying mobile devices around, but but they weren't buying handhelds to begin with. Everyone I know that previously used a DS or PSP for gaming still prefer that type of device over a touch screen phone for any sort of involved gaming session. If you have a link to research showing that core market has moved on, I'd love to see it.
Sega wasn't in good financial shape to begin with, at a time when games were difficult to sell. They lost their retail partnerships by launching console after console to compete with themselves. Sega had zero credit to ride on when they folded. Nintendo will survive.