Re: Where do you see this?
 

And notice the marine(yep, that's the main character) has a helmet!
Also, in the Alpha & Beta Demos, you could use a flashlight and a weapon at the same time, but since they were test versions, the flashlight's mesh was screwed up. :p
Of course, the F1 key would make a new light entity wherever the crosshair is...

Re: Where do you see this?
 

I suppose that id might've kept more to the style of the original Doom by keeping our marine outfitted with his helmet throughout the entire game. However, I think that the absence of the helmet shows more personality. :)