Are you talking about in the US? Because they're much larger than most of the rest of the world too!
I was pretty amazed the first time I went - for McDonalds specifically, the US's medium size for drinks and fries is bigger than our large size in Australia! And we have no super-size or drink refills. (Our Burger King equivalent is about the only fast food chain I can think of that does free refills. It's very rare for restaurants in general here).
