I don't think anyone addressed this apect of your question (if I missed it, my apoogies for repeating), but the astringent properties of witch hazel would not be too desirable preshave. The hot towel or hot water you use before shaving tends to expand the tissue (in addition to soften the beard) making for a smoother shave. An astringent tends to shrink the tissue/pores - part of the reason to us it post-shave.
