Actually, the Rift seems to be a "stand up and walk around, but don't turn more than 180°" VR - and the HMD itself isn't the problem here, as it is trackable full 360°.
Walking in a certain area is perfectly possible.
The main issue are the
controllers.
- HTC decided to trade in precission for 360° traceability; the sensors have to be positioned in opposing sides of the room in order to grant this. With this setup, the controllers will be "visible" all the time, but not necessarily with
both sensors (wich leads to less accuracy).
- Oculus decided the other way round: They want the sensors to be placed in a way they
both "see" the controllers all the time, leading to a very high precission. However, if the user turns away from the sensors, his body will obscure the controllers. With additional sensors, this problem could be worked around, but Oculus doesn't think, this would be a very widespread setup and hence not supported by many (game) developers.
SOURCE