pg had been writing about plans for Arc for several years, and so there was a big wave of interest when Arc was first released, and the forum was more active then. We've settled down for the long haul now :-)
Though, without disparaging forum contributions, I wouldn't necessarily equate leadership with the "leaders" list of people with high karma values. Many of the people who have made some of the most significant documentation and code contributions aren't at the top of the "leaders" list.
