Flying with butter or margarine?

Traveling on transatlantic flights headed to Europe, I've discovered a surefire way to confirm the direction of my flight. Ever noticed that when you travel east across the Atlantic Ocean you're served margarine, but you get butter in the western direction? The plane's food is presumably prepared by the local purveyor at the originating airport, and that determines the nature of the food. As a consequence, there usually are slight differences in the meal linked to the regional cuisine. However, butter and margarine are direct counterparts, and you seemingly always get margarine going East from the States on Delta. It's reassuring, in some ways, that the world is not yet so flat that it still maintains some degree of regionalization.

Of course, the fat content and the chemistry of butter versus margarine is equally interesting. The distinction between them is not so simple because invariably most modern margarine spreads are a mixture of butter and "pure" margarine. In turn, the fat content varies considerably, and so does the taste. Other properties, such as melting temperature, viscosity and solubility presumably also vary affecting how you cook with them. This is all to say that the underlying chemistry of these products has employed many a chemist! My apologies that I've ignored the recent Mad Men debate over how to market margarine over butter, but that isn't about the chemistry at all...