Martin Gibson, you really should read the posts above. Much knowledgeable stuff up there.

Dick Greenhaus is right about the direction of the string vibration. Good classical guitarists "plant" a fingertip on a string (press it downward, toward the soundboard) before releasing it by snapping the fingernail across the string in either a rest stroke or a free stroke. The effect is to make the string vibration as perpendicular as possible to the plane of the soundboard. All of this happens in a split second, so it's hard for someone to observe. See Scott Tennant's DVD, "Pumping Nylon."

The same thing is true of good guitarists who use a plectrum. The stroke of the plectrum should be at an angle (45^o or so), down toward the soundboard so there is a strong perpendicular component to the string vibration.

Judging from other posts of yours, I suppose you will not agree, but there is no point in arguing about this because the difference is measurable on oscilloscopes, even on an unamplified electric guitar, though the sound is so small that the ear may not be able to detect the difference.