Yeah, in its infancy, it's natural for all of the participants to be congregated on the inaugural thread. :) Comment scores for people who have the extension should show up for any comment they've made in the past two weeks, though, and it should start filling in around HN as more people start using it.
Yeah, it's a nice idea, and without an API it's the best we can get, but really it requires the participation of the majority of the userbase in order to work.