I think they're missing the point that, even if they take ultimate care of their body, there will come a point at which they can't take care of themselves anymore. Most elderly people don't go from the epitome of health to dying; there's an in-between where they decline, no matter how excellently they have cared for themselves.
Case in point is my great-great-uncle. Truly the epitome of good health. Exercise seven days a week, drink nothing but water, eat healthy, and has always been in superior health. He is currently 106 years old. For his 100th birthday, a TV station did a special on him and his healthy lifestyle, and videotaped him swimming laps at 5am, as he had done every day for the past several decades. He still lives alone. Up until he was about 104, he could do everything himself. But now his eyesight is failing and he's not a competent driver anymore, so he does need help. It's sure as heck not because he didn't take care of himself! It's because the aging process is natural. You can delay it with healthy living, but you can't avoid it entirely.