well you do stand out less in camo...duh
Sometimes you might not want your tent to be highly visible, or you might wish you could just sit still and disapear. Ever run into a hungry 500 black bear in november? You might wish you had a guilly(spelling) [a snipers cover/jacket that looks like a bush] so that you could just sit down and freeze and be invisible.

Besides that military surplus gear is rugged and for people who camp a lot and some of it not so gentle, mil camo clothes might be a good idea.
At least the pants work well for camping. Hmm - I haven't had a pair for a long time - I must've out grown them. I think I would like to get another pair for hiking in the lava out back.
Jim