Diets concern especially Americans as they do have a "national weight problem". So it would only be natural that dieting issues be so over proportioned in US. Also, "miracle diet recipes" are very popular and make way rapidly into people's minds. This also happened with South Beach Diet – diet that will not only allow you get rid of a lot of weight rapidly without starving but will also help you improve your health condition.
Being so popular, diets have even gained power of influencing food commerce and industry. If you wonder how, well, food producers that have been educated for a while to flexibly follow demands of market in order to be competitive, came out with their offer of diet-friendly product versions, attracting customers in their yard.
It seems that in countries outside US, although people have heard of diet, generally they are not very anxious to give up their eating habits in favor of a not so very well studied diet. Yet, Dr. Agatston's "South Beach Diet" book is said to have been sold to more than 20 countries.
In Canada, low-carbs diets have gained some popularity but not to extent they have in US. And this happens only at mass level. The federal department Health Canada will issue new labeling rules and regulations to prevent manufacturers from making low-carb claims for their products, as official opinion is that popular low-carbohydrate diets are nutritionally unsound.