You forget that nobody has ever played S&D, except people that played the warband beta. So for those that don't know: S&D is basically battle, except one team (the defenders) have to protect a destroyable catapult and trebuchet, the attackers have to destroy those objectives. You win by either destroying, protecting or just slaughtering the enemy team.
Oh and +1, I'd like to see this mode make a comeback.