From my own observations Mumford probably drew the largest crowd of the weekend, however at least half their audience left within the first ten songs (I'm not sure if they were heading to aftershows, or just had seen enough).
Mumford fans going to aftershows? Maybe 15% of 'em. Most probably just wanted to hear "I Will Wait" and got the fuck outta there to beat the traffic getting home.
It's a very young crowd. I'm not surprised that the Killers outdrew NIN. I started out at NIN and then went to the Killers because I like and wanted to see both. While NIN is a better band, the Killers is just happier and that fit my mood better. And considering the massive crowd at Vampire Weekend, I feel like a lot of the people there that weekend also wanted happy.