As for the fact that character doesnt exist in the Batman universe, if he was simply called Dick Grayson to begin with the ending would have been ruined, and this is a film intended to bring people to Batman, not everyone knows who Dick Grayson is but everyone knows who Robin is. Its a polite head tip to the comics whilst maintaining what was necessary to keep the film enigmatic and understandable for all audiences. In the desperate rush for prudes to criticise the technicalities of the ending, people seemed to miss the point. This was bringing together the ideologies of Christopher Nolans Batman films; that a symbol could inspire, unite and protect people through its represented indestructible nature. And thats what the ending was about; and what it achieved.