I believe the assumption is that if the number is (apparently) on the same exchange as yours, it might be your neighbour, kid, etc. and you'd be more likely to

I believe the assumption is that if the number is (apparently) on the same exchange as yours, it might be your neighbour, kid, etc. and you'd be more likely to pick up. Since most of those originate from a VOIP box in some low cost country, they do not necessarily know that this is unlikely to work in reality.