i appreciate this downvote, but millions of people have violated this copyright unknowningly... afaik this makes it invalide 'de facto' if not 'de jure'.
(Just to be clear, I'm not one of the people that downvoted you.. seems like a silly thing to downvote on when a response is much more useful to everyone).
the fact that millions of people unwittingly breach this copyright has made it unenforceable in those cases. you would expect any sane judge to throw such a case out... even before this ruling.
The problem is the lack of knowledge of rights associated with intellectual property.
Many people make their bulletin board flyers by searching a related term on Google Images and pasting it into their document, without any thought to the licensing or knowledge that they might need a license. Despite that they are not likely to face legal consequences, it doesn't erase the copyright holders' rights to their image -- even if the image is very popular and many people unwittingly infringe on the copyright every day.
TW's claim was invalid here because they did not own the full rights to "Happy Birthday to You", not because of the popularity of the song.
If something does not violate the constitution, and it has always been done in a specific way, then, unless a law directly targets it, it stays legal. (in Germany). Called Traditional law, or Traditionsrecht.
IANAL.