Jonah Nolan says..
Its a wink at the audience. Theres such a huge kind of incredible universe that writers from Bob Kane, Bill Finger, Jerry Robinson, onwards, artists and writers who created this massive universe filled with jewels, frankly. So many characters that you can never do all of them justice, he explained. But I think we endeavored to do was not the complete story of Batman but our complete story of this character. Its one of the reasons why I really wanted to see the Catwoman character there, a favorite of mine, and I think the wink towards Robin was an acknowledgement to, you like the character or not like the character, hes a huge part of that universe for 70 years.