You are right that that's how it's designed to work. But hardware controls need special features to delay a process, like a time-delay fuse is a special design. Normal hardware switches just cut the power: NOW, and let the chips fall where they may. The OS must be able to pick up the pieces on restart.
So if it takes as much as a full second, at computer speeds, for the device to respond to the button press, then the button input is going back into the OS for processing. If the software is funky at that time... "unpredictable results".
If the time delay is very short and always the same, and it shuts down hard like a PC, maybe that's in the switch... "10-15 seconds"? No way!
Perspective instantiates reality.
( By DX w/DF app. )