Do Senior Faculty Have an Obligation to Retire?

Stealing this post from the Leiter Blog (it wasn't Leiter's question, so I feel less bad picking it up here).

With the economic downturn, retirement accounts have taken a serious shot. As a result, there are going to be people who would have retired, but won't. Let's eliminate those who can no longer afford to retire and only talk about those who could live comfortably, but choose to continue to occupy their chairs just to build back up bigger nest eggs. This decision has an effect on the discipline by creating fewer jobs for newly minted grads, keeping some people out of academia, making it less likely they will publish and contribute in the same way to the discourse whereas the emeritus would still have access to libraries and colleagues and would suffer professionally nowhere near the same insult. Their decision therefore causes some degree of harm to philosophy. Is this harm something one has to morally consider or is it ethical collateral damage? Does one have an obligation to the next generation? An obligation to one's profession? Are these operative in any non-trivial way?