This all boils down to the "eat less, excercise more, saturated fats are bad" advice that has been doled out for years.
What the author seems to miss, however, is that none of the low carb authors advocate not excercising in conjuction with changing eating habits on a permanent basis. In fact, most of them state clearly that it is essential to good health.
However, according to this study excercise was seen to be not very effective at promoting weight loss, although it is excellent in helping maintain weight. This article seems to confirm that observation.

Additionally, BMI is not a good argument to show that cultures with a higher carb count are thinner. Perhaps those with a lower BMI simply have less muscle (keep in mind that body builders would be considered obese by BMI standards) and his arguments in favor of eating higher carb/low fat (The Lord's prayer?) are weak at best.