The Killing Joke is as iconic a graphic novel as they come, I don't think the same strategy would work for some lesser known titles.
Too bad the movie isn't any better, though. I buy all of the DCAU films on Blu, but this one was a letdown. They are increasingly cutting the budgets on these properties, and even The Killing Joke is a victim. It doesn't look nearly as good as 2010's Under the Red Hood.