I can understand that, situationally, there are reasons one might want to punch instead of kick or vice versa. But what mechanical advantage is there to kicking instead of punching, if any? It seems that kicking merely costs you a Combat Pool die without netting any damage increase. Due to the questionable organisation of the text I'm wondering if I've just missed something, or if there really isn't anything beyond situational constraints.
Kicks are less likely to land an effective blow, and more difficult to defend against, but deal more slightly more damage. (Plus other details, listed below.)
Basic stats listed in TROS Core Book, pg. 256, entries #3 "Kick" and #4 "Punch/Hand/Grappling."
To hit: Kick ATN 7; Kick Above the Waist ATN 8; Punch/Hand Strike ATN 5.
To defend against: Kick DTN 8 (if defending with an opposed kick/leg technique: upon successful Def roll = no damage, if defending with another limb: upon successful Def roll = damage is applied to the deflecting limb); Punch/Hand Strike DTN 6 (if defending against a thrust: upon successful Def roll = no damage, if defending against a swinging strike technique: upon successful Def roll = damage is applied to the deflecting limb).
Damage upon a successful attack: Kick Damage = ST-1 (Strength minus 1 point); Naked Punch/Naked Hand Strike Damage = ST-2; Armored Punch/Armored Hand Strike Damage = ST-1. All these strikes count as bludgeoning damage (marked "b").
ADDITIONAL RULES SUMMARY:
Weapon Length or Reach: any difference in weapon length applies an ATN penalty to the attacker with a shorter weapon (he is outside the reach of the longer weapon) until he lands a damaging blow, after which the same penalty applies to the attacker with the longer weapon (his reach has been penetrated) for both his ATN and DTN. When the user of the longer weapon lands a damaging strike the penalty reverts to the wielder of the shorter weapon. (See TROS core book, pg. 78, col. 1, para. 6).
Category 1 - "Hand" Length (fists, knee strikes) (see TROS core book, pg. 78, col. 1, para. 4; unfortunately, kicks are not listed on this chart).
I have browsed through the supplemental books (The Flower of Battle, TROS Companion) to document the "reach" of kicks, but find nothing. If I find a comprehensive chart somewhere I will update this entry (indicating if the chart is canon or optional rules).
Optional Modifiers for Striking at Different Zones (see TROS core book, pg. 234, col. 1, para. 2) apply to any weapon - including punches and kicks - to various zones of the body.
I'm not all that familiar with TROS, but researching it, there are a couple of differences.
For a punch, damage is STR - 2, or STR - 1 if your hand is covered in something hard. For a kick, damage is STR - 1, or STR if striking surface is covered in something hard.
So yes, there is a damage difference between leg and hand strikes.
Range is different, all hand techniques are "hand", leg can be "hand" for a knee or "short" for the shin/foot.
Additionally, the kick attack is restricted to zones I, II, VI or VIII.
My source for this was found at http://tros.thewestwinds.net/index.php?title=Main_Page under the combat maneuvers section.