Popular finishers are generally not copied. It's an unofficial rule amongst the performers, followed out of respect. It's different when someone starts using Shelton Benjamin's Paydirt, as opposed to something like the Pedigree or the Stunner. For guys like Shelton, their finisher is one of their moves. For guys like Triple H or Stone Cold, it has become a part of their gimmick. Because certain moves are so easily identifiable with certain superstars, it's a bad idea for another worker to "steal" someone else's finisher. It's not only disrespectful, but the fans would likely hate it, as well.
There are the obvious exceptions, like when stealing finishers is a part of someone's gimmick. Eugene using various top stars' finishers, like the Rock Bottom and People's Elbow, was kayfabe, and just part of his gimmick. Another exception would be situations like when Chris Jericho or John Morrison used Sweet Chin Music on Shawn Michaels. It was a way to get heat on them. Shawn was obviously approving, so in these situations, it is merely ring psychology, not stealing a finisher out of disrespect.
Since performers generally do not use the finishers of big stars unless it's in a respectful manner, there's no need to "retire" them. They are already essentially retired when the superstar that made the move famous retires.