Borealis wrote:
[...] there's no such thing as a North/South shortcut even on the Earth

All of this is just convention, N and S are absolute, E and W are relative. I.e. there is such a thing as a north pole, but no such thing as a west pole. North is a LOCATION, west is a DIRECTION. You could just as well have had N and S be relative (a direction) as well: say travelling "up" on a conventional map of America as well as "down" on a conventional map of China would both be travelling North.
Bottom line, no matter which direction (N, SW, E, W, NW, etc.) you travel on a sphere, you eventually wrap around and get back to where you started. This can be approximated on a "flattened" map by having the left and right edges meet, as well as the top and bottom edges. It is not possible to have such a configuration of a 2D surface in a "flat" 3D space, but it is a close enough approximation to a sphere that it works very well in games (and is much easier to program than an actual sphere). Another benefit of such a psudo-sphere over an actual sphere would be that angles and distances would not be affected (see traj's posting). Of course, Strategos believes that the Earth is flat (since it says so in the Bible), so for his sake alone we should keep the game as is.