It's not so much a high score list as it is a statistical model to rank how good players are relative to one another. The ladder system assigns players two values: their estimating competence and the uncertainty in the estimation. Each time the player plays a match, these values are altered. Beating players of a higher rank will earn you more points (increase your estimated competence) while losing to players of a lower rank will have the opposite effect. Likewise, if you play at a very consistent level, you'll have a low uncertainty. If you sometimes beat amazing players but then lose to novices, the uncertainty will be high.
It's a good system for competitive players who want to see how they rank against their friends or the world. It only works with games that have player vs player matches, so obviously, it's not possible in Dwarf Fortress.
If the suggestion is to make a multiplayer versus mode where two players can build up fortresses and attack each other, well, that's not going to happen any time soon. It would be a huge project, and it's a completely different direction from what Toady is currently working on.
Despite the fact that it won't happen, I actually think it could be rather fun to send my dwarven armies against another player.