Classic Zen involves a mix of sitting and walking meditation, so it's not all knee pain. ^_^ And the books I've read have all, obviously, been aimed at westerners, which may explain the mechanical approach. Sogyal Rinpoche says somewhere that he finds westerners want to have the process explained to them, which seems odd to him as a Tibetan because for them it's no-brainer common sense.

It might be interesting to see how it's done in Japanese and if it's at all different.