From FDA website: FALCPA’s labeling requirements do not apply to the potential or unintentional presence of major food allergens in foods resulting from "cross-contact" situations during manufacturing, e.g., because of shared equipment or processing lines.
http://www.fda.gov/food/resourcesforyou/consumers/ucm079311.htm
Manufacturers can and should take the extra steps to avoid unnecessary deaths as a result of incomplete labeling or substandard manufacturing practices. A life can be saved simply by printing a few words on a package of food.