It is interesting how popular media plays into this. On a Food Network's chef competition on chef made a typical "American" size portion for one of the dishes. The judges really didn't like that.
On the other hand typical American restaurants often insert sarcastic lines in their TV ads about how our portions are nothing like "French" portions -- you really get a bang for your buck when you eat here.
So it seems like there are 2 very different attitudes and 2 very different types of consumers. Both are catered to by different types of businesses.
I think the portion size has also been a hint as to how much a person should be eating. Those have been used more by the food processing industry to "mask" the caloric content of their products, rather than by consumers to modulate their food intake appropriately.