Islam is a poor example, as is Protestantism. Those aren't simply geographical differences, those are completely different churches. They're the same religion, but they don't follow the same religious hierarchy.
That's true, but not the point. The point was that such a feature provides the opportunity for people within a religion to develop sectarianism. Whether they choose to make it purely geographically based, theologically based, or hierarchy based would still be totally up to them.