I got to play Sedgefield with a friend in May and can see how how the pros can and will always go deep under par there as long as a) the greens remain bent grass and b) the tournament is contested in August. The greens will always be softer due to heat-stress concerns and will never be particularly fast for the same reason. There's nothing wrong with that, as I see it, but combined with the fact that the course is not bruisingly long and the par 5s are all extremely easy (everyone should birdie both of them every day, so that's two under par already), I can definitely see why Sedgefield plays easier than most courses on Tour.
That said, it's a wonderful course that I would be happy playing every day. Great set of par 3s, especially.