Why charge more for brown rice?

Anytime I ask for brown rice at a restaurant they tell me it'll be extra. But shouldn't it be the other way around? So called "brown rice" is what rice would look like if you just prepared it and served it. "White rice" is brown rice that's been polished. In polishing it, virtually all of its nutrients are stripped away. So shouldn't brown rice be cheaper?

I've always been a big fan of ethnic food as it is almost always healthier (and many authors point out the virtues of eating traditional ethnic foods for a variety of reasons). Many cultures eat polished rice, however -- the so called "white rice". It is probably the one oddity and "error" I suppose of those cultures in their food.