I'll need to see more evidence before I buy this, but a Humans Invent article by Nigel Brown avers that "Caveman instincts make you crave tiny gadgets." Brown cites a psychologist by the name of Dr. Colin Gill, who believes that
...The association with using smaller and more functional tools dates back to when man first evolved from apes. "We are dealing with, potentially, a fundamental psychological aspect of our evolution," Gill explains. "If we look at man's evolution, in most cultures men never carry bags. Men prefer to put things in their pockets, and not have any excess baggage. Some believe that this goes back to when we were hunter gatherers and men didn't want to carry bulky equipment about.
"We wanted things to be small and functional, something easy that could be hung from a belt, so we could concentrate on hunting antelopes. Therefore men are pre-conditioned to want things smaller, and easily portable. So it is men in particular who drive this design emphasis for things to be smaller."
I'm not sure it's caveman instincts so much as pure common sense that makes us want smaller objects. If I have a choice between carrying a brick-like cell phone with a suitcase battery plus a camera plus a Walkman plus a day planner plus a sketchbook plus a Gameboy, versus carrying just an iPhone, I think the better solution is obvious without having to grunt my way through it. Read the full article here and decide for yourself.