Isn't the Ctrl-Alt-Delete to login supposed to be in order to prevent a malicious fullscreen app from faking the login screen and tricking the user into entering their login credentials? (Since Ctrl-Alt-Delete is a keystroke that is routed directly to an OS handler at a fairly low level, a mere application can't intercept it.)

There's actually a sound reason, I can't really think of another way to prevent this attack vector.