Most companies have written policies about those Easter Eggs. At most major companies adding unapproved features is grounds for termination.
As Hodgman pointed out there is a huge potential for legal problems. Hot Coffee was a big one. Another bullet that was fired and missed was the lawsuits against EA by Jack Thompson claiming that The Sims 3 had explicit content when the nudity blur was removed and other cheat codes were entered; lawyers reviewed all the images in the game and found none. Imagine the backlash if a single modeler had thought "this would be funny" and included something explicit. Outside of games, Microsoft has been bitten several times; from the unauthorized flight simulator in excel making it fail government certifications, to the "volcanoes" in the 3D text screen saver getting reclassified from a feature to a bug.
From a design perspective it often does not make sense, as JTippets pointed out. You can certainly design in "unexpected moments of delight". You can also design in quests that are difficult to complete and very few players will see. The 100%'ers like to have some content that is difficult to reach, but that does not make it an Easter Egg.
It is unwise to release any untested material. Adding a hidden feature without buy-in from QA is asking for trouble.
Considering those things, I wouldn't need any countermeasures because they wouldn't exist.
Edited by frob, 02 April 2013 - 11:42 AM.