always the same v. always changing

this weekend my good friend jamie asked me a very intriguing question: why do millions of peopple eat the same breakfast every morning but the almost never eat the same dinner more than two days in a row? what makes the meal you get up with, any more habitual then the one you generally close with? i have lots of theories. one that stems from my memories of count chocula and the cinnamon toast crunch chefs leads me to believe that our good friend marketing helped make it that way. theories are as always, always welcome.