Not everyone loves the policies — or the commercials — but Mayor Michael R. Bloomberg’s emphasis on healthier living habits seems to have had some impact on New Yorkers, who now have a life expectancy of 80.6 years compared with 78.2 years for the United States as a whole. It’s too soon to tell whether the switch to healthier food in school cafeterias, and in school vending machines, has had a discernible effect on childhood obesity here. But now the Obama administration seems to be following in New York’s footsteps and is considering imposing similar vending machine rules...