Good point you have there--
I think eating 3 meals a day was a big staple of people's lives who did hard physical labor every day (i.e. farming) and it was important to eat this way since so many calories were burned. Today, many people work in offices (and other sedentary or semi-sedentary jobs) that don't burn thousands of calories per day, and hence don't really need to eat so much (but some do anyway!). Eating has become a more socialized activity, as opposed to one out of necessity. My relatives still run a farm in southern NJ and my great-grandmother used to cook from the crack of dawn to evening for all the farmers. From what I've heard, it was a never ending job for her--once breakfast was finished, she had to immediately begin working on lunch! Farming is a lot more automated now--but still a tough job, i'm sure. I would imagine those working in labor and construction today eat 3 big meals a day to keep up their strength, no?
I personally try to eat 4 to 5 small meals a day instead of 3 big ones. I feel better, by blood-sugar levels are happier, and I can maintain my weight easier. I HATE the feeling of being over-stuffed from a huge meal!