Crook led me to this post via a thread in the TDK forums, and so now I am here to offer a rebuttal in person.
The "decision" that Nolan is referring to is the one where Wayne chooses to put on a suit that makes him look like a giant bat. Nobody even in the League of Shadows had gone far enough with their beliefs to do that. Ra's even said so himself: "You took my advice about theatricality a bit literally!" Their theatricality was only used to make them seem more than human as a group, not individually. They don't make any effort to differentiate themselves from one another - they're all ninjas.
This is important because even though Batman shares many of the same work methods as the LoS, he differs from them in one major way - he has an identity.
Ra's Al Ghul, as portrayed in BB, is simply a title for the current LoS leader. If one dies, another takes over. In Nolan's version, guy with ninja skills who dresses up as a bat = Batman = Bruce Wayne. He is identifiable. If Wayne dies, Batman ceases to exist. The same can be said for Superman. Superman IS Clark Kent. If Kent disappears, a substitute cannot step in as Superman.
Having an identity makes Wayne's decision in BB a momentous one, because he's devoting his entire life to this mission, and he is a mortal human being. If there are crimefighters with super-powers already existing in Bruce Wayne's world, that lessens the importance of that decision. In fact, it almost cheapens it, making him seem like a little whiny kid who only wants to play dress-up with the big boys, when the movie says that it's anything but.