It's worth noting that both are still increasing. The rich/powerful are just increasing faster.
Something tells me this is not actually a new phenomenon. I bet the nobility lived longer than peasants in the Dark ages. Ceasers (barring a knife in the back) lived longer then the Celts north of the wall. The strong Cave man with all the food and women live longer then the skinny one bringing him the food. I'd almost bet money that a study of Gorillas shows that the Silverbacks live longer then the submissive males.
Almost like there's some biological drive to live as long as possible, and we all put a bunch of our resources into it. And if you have more resources, you tend to be more successful.