Simple answers: things like computers are faster and more powerful when made smaller. Things like engines - dependent upon volume of airflow - are more powerful when larger.
FWIW, yeah, I could stand to get rid of the ol' "big-box" computers, too. I have a mirco-ATX case and I still think it's a space hog. I'm waiting for the day when the interface you plug your keyboard & monitor into is larger than the actual area of the computer itself!
