As another Blue Bonnet commercial* from the time said: "En bread, en coo-King, no dif-fer-rance!"
Yet there was a difference, at the molecular level. Margarines were made from vegetable oils -- "hardened" by hydrogenation using catalysts which created trans-fats. You just can't say a bad word about trans these days unless you're a fat.
*I have been unable to find that commercial to strengthen my point.