It gets better--following their math, 92 minutes a week gives a 14% reduction in mortality from all causes, and every additional 15 minutes gives an additional 4%.
Clearly, it's not a linear scale. Also, this is a reduction in mortality. Life expectancy did not increase 14%, it increased 3 years which is about 4%.
It means if you exercise, the length of time you are in a wheelchair or in pain due to insufficient muscle mass (eg. chronic back pain, or chronic joint pain, etc.) is greatly reduced. Instead of a slow, painful decline leading to death spreading over last 20 years of your life, your life ends much more abruptly. For example, you die from complications to some cold virus while you were fine just a week ago.
Exercise is about quality of life, not about its duration.
True true. But also the quality of your life is usually improved due to exercise cause of increased neurotransmitter release, hormones, etc. A little bit of exercise should improve quality and duration of life by a someone positive percentage. In theory anyway.