Its about whats important to the summary of the plot of the film Knowing that his legal name is Robin is not because its an inside joke to fans of the character We know this was just an inside joke because its been stated so by Jonathan Nolan and JGL It wasnt intended to be more than that With Moneypenny thats borderline because thats not a code name or alias for the character in the series thats just always been her name None of the Robins have ever been called Robin for their actual name Thus were pointing out a joke that is only relevant to people that know who the charater is as well as applying a significance to that fact that is otherwise not indicated in the film itself the OR part comes to us applying a significance to the name solely because we know who Robin is in the comics