That's what AnyDVD does. It figures out the key.
As to why there's a box that lists the keys... all CSS-crackers have that box one place or another, I suppose for those that are overly curious or for debugging. Maybe some people somewhere swap keys around from program to program. I know that some programs get stuck finding some keys, maybe this is an "in case program X can't figure this key out" sort of thing? I dunno.