the way we now see new posts/replies seems 'bass acwards'.
That's why it's perfect for Which Witch sWitch Week!
And isn't it great that the YaBB SE developers had already built such a feature into the system?!
It's almost as if they knew Which Witch sWitch Week would be coming even before we did!
Seriously, though, sorting posts newest to oldest is a feature on many forums. Not all systems have "new" icons or a feature that will automatically take someone to the most recent post made since the last time they've read a topic, so it's much easier for people to locate the newest posts if they're sorted that way. The SE developers most probably included the feature so that people who are more used to/prefer it that way would have the option.