why does turn off button means hibernate on my win8

when I upgrated my laptop's system to win8.*,I found it's hibernate when I clicked turn off button.

but sometimes you need restart your computer.if you don't like this,you can change it.there is a new function which called turn on fast startup in win8.it's on by default.you can off 'turn on fast startup'.

you can find option here,Control Panel\Hardware and Sound\Power Options\System Settings