Welcome to Android Central, and sorry for the delay! You're doing two different things there. A short press of the Power button makes the tablet go to sleep, not power off. So the device is in a suspended state, and can turn back on quickly with another short press of the Power button. The screen typically comes on when the power cable is connected as well in this situation. In sleep mode, background processes can still occur, so the device could still refresh email or Facebook updates, for example.
A long press of the Power button and then selecting Power Off turns the tablet completely off. When a device is completely off, nothing is happening within the system.
What do you mean by making the light press the default? You want the light press to power down the tablet? Wouldn't you find it inconvenient to wait for it to boot up each time you wanted to use it? Remember, the boot process can take upwards of a minute or longer on some devices.