It's not using simple stereo screens, they have lightfield projectors:
Project HoloLens is built, fittingly enough, around a set of holographic lenses. Each lens has three layers of glassâ"in blue, green, and redâ"full of microthin corrugated grooves that diffract light. There are multiple cameras at the front and sides of the device that do everything from head tracking to video capture. And it can see far and wide: The field of view spans 120 degrees by 120 degrees, significantly bigger than that of the Kinect camera. A âoelight engineâ above the lenses projects light into the glasses, where it hits the grating and then volleys between the layers of glass millions of times. That process, along with input from the device's myriad sensors, tricks the eye into perceiving the image as existing in the world beyond the lenses.
They track eye movement and adjust for that as well. I think you need the lightfield stuff so that the eye if forced to adapt focus for different distances, it's a depth cue that Oculus don't have.
It'll be interesting to see what frame rate and latency they achieve. It sounds like they have a lot of hardware in the headset, so it could be quite good. Plus they only need to render the bit right in the centre of the field of view at high quality.