there is a lot of truth to this, but there are some issues surrounding things like upper or lower abs, but these things are due to postural differences not actual size of the muscle (although the specific muscles can be strengthened to get a postural change which is beneficial allround). for example, some people have an excessive arch in their lower back. this can be easily corrected by PROPERLY isolating the lower abs and stretching the lower back, hamstrings and calves to bring the body back into alignment. such things can be caused by flexibility imbalances, muscular imbalances or a combination of the two. actually alot of the issues raised in this article are generalizations that break down because everybody is unique in their physique and associated imbalances. i suspect that these generalizations arise from people who are successful because they don't have such imbalances.
anyway, here are some great articles to read about ab training from ian king: