I will search for it and post it when I find it again, I'm sure I have it bookmarked somewhere but I'm at work right now.
But just think about it, the biomechanics of the area and all of it. When you slow down and stop just a parallel, its all in the knees. Sure the muscles contract to stop you, but most of the stress from it is on the knees, where the tendons and ligaments are being pulled and tightened to stop.
When you squat ATG and sit back properly (which most people can't do w/o a heeled shoe), all the stress is shifted to the glutes and/or hamstrings.
Plus, in my personal experience, after starting to squat PL style, really wide and sitting far back and keeping the knees behind/over the middle of my foot, I ended up injuring the knee, and coming down with tendinitis.
I took a month vacation from lifting (because I got tendinitis in my wrist from benching), I started training for OL, and my knees and wrist haven't hurt since. If anything, my knees are a lot strong from squatting lower.
I'm just basing this on what I've read from a reputable study and from my own experience.
And Hanley, OL might use less then their true grind out 1RM for squats, but we also squat a LOT faster then PL. PL is under tension for a longer time generally that would put even more stress on everything.