There must be something else in it that we haven't even thought of. Nintendo knows that Sony is an electronics company first and foremost, so it would be easy for them to throw a 3D screen in a hurry. They also know that Sony have absolutely no shame in ripping tech right off Nintendo.
I have a feeling that come E3, Nintendo will have one hell of a curveball lined up that will catch everyone with their pants down (see Wii). I am probably wrong, but they have done it before, so there isn't really a reason they wouldn't do it again.