I guess grains and milk products get such a big part, because the food-guide pyramid was created by the department of agriculture. I think milk and grains are the most redundant produced nutrients.
The paper of Rozin, Food and Life,Pleasure and Worry, Among American College Students: Gender Differences and Regional Similarities is very shocking. One the one hand it is good that a healthier lifestyle is promoted and recommended in every media that everyone get aware and get support to develop a heathy lifestyle. But on the other hand all the information offers less confident persons, or nutrition aware people to many factors they need to concern about.