Someone in AeroXP has disovered a new feature in Windows Vista called away mode.
What is away mode?
“Away mode is a unique power state that is new in this version of Windows. In this state, your computer appears to be shut down. The monitor is off, audio is muted, and moving the mouse or typing on the keyboard has no effect. The computer requires no human interaction but is fully operational to do things that should not be interrupted or stopped, such as recording a TV program, burning a CD, or hosting a multimedia broadcast for remote users. While the computer is involved in these activities, Windows temporarily prevents the hardware power button from putting the computer to sleep or shutting it down if the button is accidentally pressed.”
More About it over here
So we might be seeing this in newer builds