Thats not the case at all. There is a really big difference btwn a Carib grad, and an actual IMG, or a foreigner. If someone is American, and went to the Carib for school, and receives a crazy score, 270+... There are not going to be many doors, if any that are closed. Actually, if someone gets over a 240, I know for a fact that American medical schools are very open to allowing them to transfer in and do rotations along with the rest of the class, and graduate as an American Grad! (ie. American University of Antigua, has a part of their site about students that actually did that!)Besides, if you have a great score, personality and recs, nothing can stand in your way. A 270+ throws all "stigmas" out the window..
If your a actual foreigner, than thats a different story, and they may have some difficulty but alot can be over looked with a score like that.