Yeah, but there must be some way out, Michael and Walt left in the skipper from a designated point following a prescribed course, he'll make it out but not far. We know there's some contact with the Island from outside, there was a food drop, where did the plane come from, near or far? Does the Barracks have an air strip, is it an aircraft carrier?
It's possible the Hanso Foundation/ the Darmha Initiative/ the Widmores are aware of the island's inhabitants and the Barracks is the connection between the Island and the outside world. Penelope Widmore, Desmond's missus, is aware of the Island's existence from her families involvement though she almost certainly doesn't have influence, those Arctic researchers at the end are her own, not the Initiative's. Her father obviously used his influence to send Desmond in it's direction. The island is designed to draw people to it's shores and keep them there.
Any one else see this?