I agree with the others; some horses have had abuse, and may or may not be head shy. Some horses have had no abuse, and just are head shy, because they are just more leery of hands, and such being in their faces.
My mare had definitely been eared at some point before I got her, because you couldn't touch her ears or poll area with out her cringing and pulling back in fear. I've just taken things slowly, but I DO touch her ears, and her poll...she is 100 times better than she was last fall when I got her...I couldn't bridle her without her anticipating being eared, and trying to get away. Now she lowers her head, and lets me bridle and unbridle her with little issues; everyonce in a while she'll have a 'spazz attack' and I will just spend some time desensitizing again, and that will be that.
So my advice? Whether he's been abused or not, make it a point to touch him everywhere. Use approach and retreat methods if you have to, until he is comfortable with you approaching his head, but DO touch him...I think of it this way; if I ever have to have a vet do something with his head, I don't want to have to sedate him, just because I never bothered to help the horse overcome his fear...so even if you are okay with him being that way, make sure you work toward helping him get over it, so if someone DOES have to work on his head, ears, and face, he is okay with that.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."