Dreamcast failed because Sega didn't know how to market it. It astounds me, because the Genesis kicked the sh*t out of the Super Nintendo back in that era of the hardware wars. They obviously did something right.

I believe Nintendo will continue to succeed because:

1) They have the best first party games of any system out there, and that cannot be disputed.

2) Their niche fanbase is incredibly strong. Sure, they cater to a younger age demographic then the other two systems, but they knocked my socks off (as well as many other people's socks) with Resident Evil 4.

3) The Gameboy (and all it's iterations), not the PS2 or Xbox, has lead the console wars for the past 15+ years. Sure, Gameboy is not a home console, but I truly believe it's the Gameboy that is keeping Nintendo in the big picture more than anything else. As long as the Gameboy (and the new DS) continue to succeed, Nintendo will always be a force to be reckoned with.