The implication I've always gotten, from what I've read, is that, for all that his life as Batman is all about violence and long nights and fighting maniacs, he's still gotten to do things that few others have, helped save countless lives, and generally had a fulfilling time of things. Basically, being Batman is REALLY cool, and an expression of his basic self, and he doesn't want to be just plain Bruce. There's a sequence at the end of 'Knightfall', where he's healed from his broken back and is trying to get back in shape to fight AzBats and reclaim his position. He's standing atop a gargoyle on top of Wayne Enterprises, and remembers how his final test as a beginning vigilante was being able to jump from that perch, cast out a line at exactly the right time, and swing onto a ledge. It took a certain something, a certain confidence in oneself, to be able to do that, and he's afraid that he may have lost that certain something. He thinks of life without his alter-ego, of "remembering what I once was - and could never be again", and it scares him. He walks away from that gargoyle then, and it's not until later that he finally gets the confidence to make the jump successfully - and once he has, he has a satisfied look on his face, like 'oh, yeah. I'm back in the game.' That says it all for me.