Sure it does. But only pitch and yaw (turn head up-down and left-right for you non-flyers).
With six degrees of freedom you can move your head sideways and up or down (think raising yourself up to look over a crest).
Get a TrackIR, then you just turn your head a little bit to see the mirrors. I's great for immersion, but then I also have a widescreen monitor so I can see the mirrors most of the time anyway.
Now we only need full support for 6DOF...