It hasn't, just like the growth of abandonds, though that is more likely to happen.
*cough*
Yeah, expressing opinion again, but picking your starting direction not only makes the world look a bit 'uneven' ie - overpopulated north, but it also makes everything a bit too easy for pre-made tribes. I'll use 'die' from w10 as an example, they were able to play with each other even more succesfull becase they were all in short distance of each other. Then if you look at halp! and Se7eN on w13, you'll notice a big difference. Admittedly they're both top tribes, but they're fighting to survive, not fighting to conquor everyone else.