Close one eye and focus on something really close with the open eye. Notice that things that are far away are blurry. Now still with one eye open, focus on something far away, and notice that things nearby are blurry. VR doesn't replicate this.

This is a very active area of research, and I'm pretty confident it will be a standard feature within the next five years. There are also light field displays, which are super interesting, but I'm pretty sure they are cost prohibitive for consumer devices.