I know why the winters last so long in Game of Thrones. The credit sequence shows that the curvature of their world is opposite of ours. You can see that the world curves upward when the camera pans across the narrow sea towards the Dothraki homeland, as if on the inside of a globe instead of the outside. In other words they live inside a giant Dyson Sphere (http://en.wikipedia.org/wiki/Dyson_sphere) in the distant future. The massive size of the sphere accounts for the length of the seasons.