If you want no HUD, just leave your computer and have a look around ;-)
Actually, removing a HUD doesn't always give you more realism and immersion - in the case of a health bar, how else will you tell what your physical condition is? In real life this is conveyed by the feeling of pain, and I don't think anyone will ever extend virtual reality this far. So unless you're wearing a belt that inserts needles into your side to represent your health level, I think a health bar is still an important part of any realistic game (unlike something like COD2 where the player magically "heals" in a few seconds from serious bullet wounds).
Now, of course, HDTV screen burn is an important issue, but totally unrelated to realism.