Why choose that birth name for John Blake?

Analyzing the past two films and Rises, Nolan (Director) and his brother Jonathan (Screenplay Writer) are trying to envision a world where they asked the question… "What if... Batman existed in our current world today as opposed to the comics." Thus the feel and directing has a less comic book-ish (if that's a word) look, and more of a real world view.

This film take on Robin is quite incredible when you think about it. Like the previous person in this article wrote, he is an embodiment of all the Robin’s in the comics. In contrast you have Nolan’s Robin (John Blake) who is, at this point, the first Robin “Dick Grayson” to Batman. He’s referred to being hot headed and angry like the Robin “Jason Todd”. For the “Tim Drake” Robin… well, he was the one that was able to deduce batman of his true identity and was also depicted as an orphan. And with the film using elements from the “The Dark Knight Returns” comic by Frank Miller, the role of that Robin was a female “Carrie”.

The whole point of Nolan's Batman is a meditation on myth and legend. He includes these things to imply, I think, that the version of batman we learnt about over the years is a myth based on some things which may or may not have happened, events passed on by word of mouth and stories. As in all myths, names change over time, get jumbled up, and the story changes like Chinese whispers. so Nolan's version is one telling of the myth. The next director will tell another version.

In one version of the myth Robin is his side kick, in another his successor. In one version two face carries on damaging the city symbolically due to the draconian laws past as a reaction to his death and the lies his death propagates which eat away at the soul of Gotham; in another myth he literally goes on damaging the city as a criminal. It's kind of like the various gospels in religion.

I think Nolan left it in the idea that Batman is retiring and wanted to end the saga unlike the comic book stories which run infinitely. He wanted Blake to take over the legacy from Batman and probably plays a little homage to Robin like Ducard's reference from the comics as pointed out earlier.

Also using Dick Grayson would've led people to believe before the movie that we might see Robin that's also another reason why they had to wait til the end.

I took the mention of his first name being Robin as a sly joke. He is an amalgamation of all the sidekicks Batman has had and was essentially the Robin character in spirit. The problem was that the dynamic between batman and robin had become so campy and ridiculous in the film representations they needed to approach it in a fresh way and not have him deck out in tights and run around after bats. So he could be taken as a Robin character and also can become the Batman much like Dick Grayson did in the comics.

Because some non-comic readers aren't familiar with Dick's name, and Nolan didn't have the sense to reveal his real name as Grayson and throw in a line about him being a Boy Wonder (which would have clued in the audience AND satisfied the fans).