Revealing mistake: When Dae-su enters the room of one of his nemesis, his computer screen shows information about the stock exchange. The Internet address on the screen is: C:/DocumentsandSettings/[.]/OldBoy/[.], which would be a link to a folder on that computer, not an Internet address.
Revealing mistake: When the man holding the poodle leaps to his death, as his body smashes against the car, you can easily see that the poodle in his arms is just a stuffed doll, based on the way it bounces and moves.
Revealing mistake: After Oldboy takes care of the guys who turn up in the elevator to beat him up, the exit door opens in the garage, and all the knocked-out thugs fall out or down in the elevator. However, one puts his arm out to stop a hard fall to the ground, even though he is supposed to be knocked out.
Revealing mistake: Towards the end of the single-shot fight scene, you can see Oh Dae-Su visibly miss at least two punches by several inches. They go by quick, but they're there.
Answer: Perhaps because in the movie/book "The Count of Monte Cristo" that's what happened to him. In the book/movie the hero Edmund Dantes is renamed "the Count" in order to disguise that fact that he is Dantes after having broken out of jail. This way he is free to seek revenge on the ones that put him in jail under false charges.
CCARNI ★