I would concede the point if only due the one solid piece of evidence that can sustain your claim: namely Bruce's injuries. As the doc that checked him out showed us, he was in pretty rotten shape, what with having no cartilage on his left knee, contussions on the kidneys, shoulders and even his brain. Not to mention whatever damage Harvey's bullet caused followed by a 3-4 story fall (which could've caused any or the injuries listed above, mainly the one on his leg). Perhaps after he limped his way out towards TDK's end credits, he simply was in no physical (or mental) shape to continue anymore... BUT...we're talking about the goddam Batman here. A very driven individual that perhaps managed to endure that and more because he could, indeed, take it. Thus he kept on going incognito if only for a little while longer, hanging up the cowl because he was no longer need or because his body simply could not go on anymore. We are debating and conjecturing over something the film only treats superficially and with an eight year gap to consider between the events of both movies. We both don't know everything that happened during that time. If you have something that clearly flat-out states that he hung up his gloves that night, then feel free to post it here and we'll all shut up.