Doing the kind of IT roles I do for a living I am typically staring at a computer screen. What I am looking at are large amounts of text and numbers, jumping between applications, sites and consoles while keeping track of multiple things and problem solving for anything I see to be out or place. (Sounds exciting, I know) I am not unhappy or angry when I work but I don't tend have a very friendly look on my face in it's resting state or when I am in deep thought/ concentrating. I feel this is normal for me and am fine with how I am. Also I think it would be creepier to see everyone smile all the time. Though there has been times in the past where certain people have annoyed me by asking at the worst time if I was angry or what's wrong...
I have some advice, if you do see someone not smiling, don't ask why they are not smiling or what's wrong, instead try to make then smile. Tell a joke or something funny, give a complament ect... this is a much more pleasant distraction.
Random photographic proof I smile
(Face covered to protect the innocent)