Galaxy's API goal is to be intentionally stateless, and methods that operate on a history accept that as a parameter and don't recognize the notion of 'current'. State like that is to be maintained in the client, whatever that is -- whether a webpage, cron job, etc. I think this approach is probably *more* flexible in that we don't box ourselves into relying on the notion of a 'current' history, though some few methods might currently rely on it.
It's worth noting that this argument has conspicuous parallels to the argument against allowing tools to understand the 'current' history as well.