Culture Makes a Huge Difference!
Despite witnesses' frequent claims that they are unitedly the same in their teachings the world over, there are significant cultural differences in the way congregations "enact" Watchtower doctrine.
For example, I heard that the Scandanavian witnesses are not strict in the shunning of disfellowshipped witnesses and that in some parts of the USA, a much more hardline approach is taken in disciplining wayward witnesses than in other perhaps more liberal parts of the States.
Imagine how the reported variation could change and increase over time, leading to major differences in the treatment of ex-witnesses.
Another source has reported that one of the main reasons the JWs have not increased in the Pacific Islands is because many of the Island cultures are fiercely family and church oriented and they would never tolerate the hardline policy on shunning family members who have left the religion. On a lighter note (I hope) I've also heard that the Watchtower has "accidentally" spawned a number of breakaway nutty religious groups in the African states of Zambia and Mozambique. Any confirmation?