The stunning shortsightedness and obtusity of XEROX's top-level suits has been well anatomized in "Fumbling The Future: How XEROX Invented, Then Ignored, the First Personal Computer" by Douglas K. Smith and Robert C. Alexander (William Morrow & Co., 1988, ISBN 0-688-09511-9).
Xyzzy has actually been implemented as an undocumented no-op command on several OSes; in Data General's AOS/VS, for example, it would typically respond "Nothing happens", just as ADVENT did if the magic was invoked at the wrong spot or before a player had performed the action that enabled the word. In more recent 32-bit versions, by the way, AOS/VS responds "Twice as much happens".
The popular `minesweeper' game under Microsoft Windows has a cheat mode triggered by the command `xyzzy<enter><right-shift>' that turns the top-left pixel of the screen different colors depending on whether or not the cursor is over a bomb.