Science also says Polar: http://en.wikipedia.org/wiki/Polar_climate
We certainly don't use "arctic" here in southern hemisphere, well, at least here in Brasil. We say "polar" for Antarctica.
Bizarrely, even under the Köppen System*, where 'Arctic' is defined* as 'Polar', its still keeps 'Subarctic' as a category.
Anyway, my point remains that it is not something that D&D has made up, it is how a lot of systems refer to the region.
*Which interestingly focuses on climate as a feature of terrain, and is probably the system closest to what were looking at.
**probably sensibly