I blame Hitler
Okay how many Brits have been to the good ol' USA? Seen the portion sizes? It seems all, but the most snobbiest, establishments seem to equate quantity with value for money. Of course, with waiting staff living largely on tips, and lower transportation costs, US establishments can afford competitively larger portions. However, watch the average 'joe' eating; by average, I specifically mean not the spherical, trailer trash, morbidly obese specimens visible on Google Earth. Average Americans are content to leave half a starter, pick over a main, scrape the top off of a desert and, maybe, ask for a doggy bag. Why?
Perhaps food is just cheaper with respect to higher disposable income, but also when did the USA have food rationing? A generation of Brits were brought up to finish everything on their plate because there was a war on. They passed this sentiment to their children who in turn have maintained it until it has passed into social norm. The simplistic cure is smaller plates, smaller portions and, for restaurants, smaller bills. However, the real challenge is educating people to eat according to their needs and not simply consuming whatever is served up to them. To illustrate the ludicrousness of the current catering situation one Italian restaurant chain offers a 'lower calorie' alternative to several dishes at a higher price; so ordering the normal version and simply not eating all of it, and saving some money, could never be an option then?