Yes, judging is work. Yes, you pay to go to the conference, so yes, you pay to go work.
But, I find it rewarding, and fun to go judge in the "biggest of the big league competitions" with a bunch of judges from all over the world. You do learn a lot simply from all the interactions. You also kind of get a vicarious dog in the hunt, seeing if the beers you advance end up doing well in BOS.
Besides, its only 3 hours or so. I can spare that.