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).