Yeah- it was a pretty standard thing in Desktop Managers for a while for <C-Alt-Del> to be logout (or return to DM, depending on what you're using). I think GDM 3.0+ finally threw it out, but you'll still see it in KDM, LightDM, and Slim.
On a side note, ctr+alt+backspace used to kill Xorg (still can if you enabled it - but these days that shortcut key is disabled by default)