This makes me wonder if there are easier ways to get more blood flow to the brain and enjoy the protective benefit, such as sleeping with your legs up every night, or showering with very warm water every morning and evening.
The assumption is exercise results in higher blood flow which does "something". I know its easier to concentrate when you have practice concentrating, and for many boring people, exercise might be their only daily experience with concentrating, aside from the rare occasional dementia testing. Possibly forcing concentration on a regular basis (via exercise, or whatever alternative) results in better cognitive test results.
I suppose a lot depends on defining exercise as staring at a TV while walking on a treadmill vs playing racquetball.