In an interview, Roy said that the particular case study was not typical, although it highlighted the dangers of not preparing well for retirement. The subjects wanted to retire at 62 rather than 65 and were heavily reliant on their portfolio, did not have a pension, and were in their peak earning years with a very high savings rate toward retirement, but also had a higher-income lifestyle. 

"We were surprised by the degree to which those three years had importance for this particular case study," Roy said. While she stressed that "everyone's situation is unique," in this case, "those three years were incredibly important" — with each additional year of work contributing to three years of retirement coverage. 

It wasn't just the loss of those three years of peak earnings, but also the fact that they would be tapping their portfolio three years early, losing three years of savings and locking in Social Security benefits at 75 percent rather than at the maximum that added up to such a huge impact. 

Retiring at 62, said Roy, is the "actual experience" these days, although many people say they plan to work until 65. "On average," she said, "people retire at 62 across all wealth segments," although the affluent may be doing so to pursue other interests than work. 

Also read: 401(k), Social Security should be enough for most retirees

Roy said another factor that the affluent often fail to take into consideration is longevity. If they have a predisposition genetically to live longer, from a professional perspective they could outlive standard projections. While studies indicate a typical life expectancy of approximately 86½, the affluent, in good health, could easily reach 90. 

Said Roy, "One thing to focus on a lot at the front end is to make sure you're planning for the right time-horizon long term." At least some of the affluent could be facing a potential 30-year retirement horizon, so they need to take particular care that they won't outlive their money.