Fact: Cena and Orton have had a number of rivalries over roughly ten years. Often for the world title. They used to work really hard to make them bigger and better, but they were never really... good. The reason a finishing move is usually a finishing move is that hte one who performs it can do it to almost any person at almost any time. The Stone Cold Stunner, People's Elbow, Hogan's Leg Drop, Benoit's Diving Headbutt, Mankind's Socko Claw... the list goes on and on.
Because Cena's AA(Attitude Adjustment) and Orton's RKO(I think it actually stands for Randal Keith Orton) are both really simple moves to perform or sell, on a number of matches for the sake of making the match seem bigger and better, they performed each-other's finishing moves to make the match seem flashier.
So Cena actually has performed an RKO outta nowhere at least two or three times. Normally to a chorus of "Boring, Boring" by the fans, who have a natural distaste for the 35th installment of Orton vs. Cena.