Just as a side note on Sony doing 3D on the PS3, and why some people may have thought that it was pointless ...
Without even considering the likelihood that the PS3 could produce similar graphics to what people have become accustomed to while supporting 3D displays, the big advantages the 3-DS has over a home console is that the 3D display(s) are included in the purchase price of the system. At this point in time, there are so few people who have 3D displays in their homes, so many people who recently (past few years) bought a HDTV, and still so many people using a SDTV, that a feature like 3D output to a TV is never going to be used by most people who own a PS3. In a lot of ways you could see this as being similar to the N64 being able to support HD resolutions; while people might think it was a cool feature, most people would concede that it was pointless at this point in time.
As I have said before, I do agree that this may not be the only improvement that Nintendo has in store; and the reason I think this is that a 3D display seems like a very conventional enhancement compared to what Nintendo has done in the past. I do admit that this could be the major difference between the DS and the 3-DS. Nintendo may believe the theory (which I think has merit) that the industry alternates between evolutionary and revolutionary generations; and while the DS and Wii were fairly revolutionary, their successors could be evolutionary improvements on what they provided.
