Comment by SapphireSun

It could be a sample size effect. There are all these old people there, but how many? It may have nothing to do with the island, they may all have just been lucky and had a streak of heads in the coin flip game. This is especially likely since the researchers are looking all over the world for these small pockets of longevity.

Why don't you ever hear about these things in larger areas? Certainly different countries have very different lifestyles. What's different is that bigger regions have a smaller chance of a freak streak of long lived individuals as a proportion of the population (though as an absolute value, you'll probably find more).

I suspect "blue zones" will regress to the mean after these individuals in the study die, but you can never be sure. If they don't, maybe the islands do have an effect (or maybe they started to attract immigrant older people seeking longevity).