Here's the real reason why the Japanese summer vacation is so short (for many, it's a matter of four or five days): the natsuyasumi (summer break) is essentially full of stress and if it were any longer, people up and down Japan would likely pop veins en masse.

Ah, natsuyasumi. For many of us, it means getting up at two in the morning to beat the traffic, cram reluctant offspring and loads of luggage into the car and drive for long hours on freeways crowded with other family cars while periodically yelling at the kids to shut up back there. On the way, the resto eria (rest areas) and the famiresu (family-style restaurants) are full of people, and every tourist hot spot is incredibly crowded. All this attests to the Japanese love of packing a month's worth of amusement, stimulus and rest into the space of three days and calling the whole thing reja (leisure). Reja has been an honored tradition for the past five decades now, and those who don't partake of the experience are seen as henjin (weirdos or cranks).

It wasn't always like this -- in fact, in the prewar period, most people had only one and a half days off per year. This was to observe obon (when the spirit of the dead come back to visit) and to go on the ohaka mairi (the visit to the grave of one's ancestors) with family members. It was the time to say a few prayers, pull up the weeds around the hakaishi (gravestone), and reminisce about the uncle who died young. That done, everyone would go back to work without complaint.