<< Actually, I was reading this book called "Fast Food Nation". >>
I read an article I think in U.S. News that was basically discussing the same issues as Fast Food Nation, that book was mentioned in the article.
Anyhoo, the author described all of these "upsize" schemes are to get you to eat more, so that you'll become accustomed to eating more, and more, until you're a fat cow with dangerous cholesterol.
The cost of the additional food is already built into the 'base price' of the meal without the upsize. That's why the base meal costs you $3.79, but you can get like 50% more food for 40 cents? How can that be, unless they are already charging you for the upsized amount in the base price. That's how upselling works in almost any industry, really.
I order the base meal, no upsize, and usually I try to make due with the single or junior sandwich instead of the super double meat double grease version. Took a while to get used to, there is the urge to go with more food, but we really eat too much in this society.