Actually, I don't actually see a copyright notice on the actual minecraft product. I haven't downloaded the actual zip (I don't have minecraft at work!), and ma

Actually, I don't actually see a copyright notice on the actual minecraft product. I haven't downloaded the actual zip (I don't have minecraft at work!), and maybe there are additional claims there, but the copyright string on the page is simply the required acknowledgement for the original Ordinance Survey data under the Open Data license that you linked. Note that the Open Data license does not require that your products based on the data be open as well, just that you acknowledge the source. The Minecraft world is built by the British Geographical Survey, not the Ordinance Survey.