pdrusch,
Are you sure about that? Long time since I flew the 767, but my last types have been 737NG and 777 which I thought operated in the same way. I think you can engage the A/P without the F/Ds. It engages in basic attitude modes, and then goes into whichever mode is selected.
I'm not sure that "The A/P follows the F/D" is exactly correct. Rather, they both get inputs from the AFDS system.
As to the original poster, you've mis-interpreted something. The only things that can move the flight controls are the Pilot and the Auto Pilot. As Luvely said, LNAV and VNAV are AFDS modes that drive either the F/D or the A/P. They do not autonomously fly the aircraft.
Oh and luvley, not every airline has 757s AND 767s. If got 3500 hrs on the 767, and I've never SAT in a 757!