I think having a hud is another `inherited` un-questioned copycat feature often added without being thought out. Like many have said, the game world itself should convey what you need to know, do you really need to separate-out a layer of information floating on top of the screen making it not look like a real environment but instead an environment hidden behind a panel? That said some types of games you must have the hud, such as a radar. HUD's usually seem to be about `technology` and ways of getting information that can't be transferred visually, but then, building in say an infra-red vision thing in the real view of the game world would be more `wysiwyg` than a little map in the corner. I think maybe there just wasn't enough technological advancement before or CPU/GPU power to be able to directly represent status in the game world itself, requiring small and easily rendered floating stuff.