Why does some Lowfat Milk contain One percent fat and other Lowfat Milk contain Two percent fat?

Determination of Fat in Milk, Bulletin LXIMost cows naturally produce milk containing from 3 to 5 percent butterfat. In most states, "whole" milk is defined as milk with at least 3.25 percent butterfat. Lowfat milk, then, is any milk that falls between .5 percent (skim or nonfat) and 3.5 percent (whole).
   In practice, 1 and 2 percent milks are the most popular types of lowfat milk. In fact, we've never seen 3 percent milk, probably because that one half a percent would not reduce the calorie count enough to appeal to dieters.
   Many customers were sick of looking at what looked like water residue on the bottom of their cereal bowls; lowfat had been steadily gained market share for the last thirty years, stealing customers from both skim milk and whole milk drinkers. In fact, lowfat milks outsell 'whole' milk in most parts of the country. Two percent seems to be winning the cash register battle against 1 percent, but not without a cost to the waistline; that extra percent of fat adds about thirty calories to each cup of 2 percent lowfat milk.www.annecollins.com/calories/calories-milk.htm