There's no special "low level feature" when your keyboard hangs off a serial bus (as did pm keyboards from the start. XT, AT, PS/2, USB...) As far as I know also C-A-Del was just the default in the original bios keyboard handler to trigger a quick reboot.

Windows, for example, has a (by default disabled) feature to trigger a kernel panic on Ctrl+Scroll lock. Also purely software based and just as arbitrary in its choice of keys. And also very useful to recover from an otherwise stuck system.