ash can also be used to 'remove spirits' can't it? I am also pretty sure that first EW article on here states the same things.
Just saying there are 2 islands and that the others are there doesn't make a lot of sense considering they were already on the main island before locke/ben split up, right?
We have also seen that apparently the others just walk around any time they want around the island, unless you believe that was something jacob is throwing out there with a stuffed bear dragging behind.