Mark Ci , Nov 23, 1998; 01:54 p.m.
This has been beaten to death here several times, but the real information has usually been lost in a sea of yahoo speculation, so I'll repeat it.
The "discrepancy" is not due to stereo vision. It's due to the fact that, to achieve natural perspective, a photograph must be viewed so that it covers the same angle of view as the scene did when the photo was taken. An 8x10 held at 12" from your face covers about a 45 degree angle, so to achieve natural perspective under this assumption, you need to use a lens that covers the same angle -- about a 37mm. Change your assumptions about print size or viewing distance and your "normal" lens focal length changes.