Americans have larger drinks than any other nation (except for Australia and beer). We are also pretty much the only place that gives free refills. Soda is so cheap that you pay for the cup and the actual soda is free. If you go to Europe, not only do you get a smaller cup, you are charged another $2 or so for every refill.
I come from the desert. I drink a lot no matter what. I would end up broke.