Is creamer used in countries that don't regularly have milk in the fridge? I've never heard of anyone using it in Australia, but I've also never seen the need when everyone has milk and sugar readily on hand.
The 'advantages' of creamer as opposed to actual dairy are generally being lactose free (though they do contain casein), longer shelf life, and coming in a variety of flavorings. If you also include the powdered kind then you have the advantage of not even needing refrigeration after opening. I've seen many a waiting area or office where they have a can (or tub) of the powdered stuff offered up next to the cheap drip coffee being provided.
I think it's just how they drink filtered coffee. I mean, I've drunk my fair share of filtered coffee but with a dash of normal milk and no sugar. So I think adding creamer is a similar approach (although I'm not positive it has sugar in it).