Your data is missing a "physical security" dimension. I don't think Medellin would be in your top 20 if this was taken into account. It wouldn't have to be a kidnapping or mugging - just having your laptop robbed would be disastrous for a nomad.
Medellin is (i think; never been there) a rather modern city, so it might be a bit easier. Still, charlesmchen's concern is valid for most south-/cental-american listings.