On average wealthier people live much longer than those who are not wealthy. This study only surveys people who have been retired for two decades. Because that is a long time to live after retiring, the study could be skewed. It may have sampled primarily wealthy people. The financial markets in which wealthy people have their savings have been on a 10-year-long rise. Wealthy retirees who still have money in stock markets, are doing quite well in those markets overall.
It would be great, if all retirees were able to grow their retirement savings. However, it is probably not a good idea to count on it.
