tomBitonti
Hero
One style in one book does not a MUST make. What you describe sounds rather like what I see in some forms of recreation fencing - it is not generally used in the heavy-armor fighting I have seen.
Generally speaking, the strike against the arm/hand you mention is not easy - at the time you can target his arm or hand, his weapon is leading and coming at you - you have to get around the weapon to get at the arm, and trying to do so generally means you are open to getting hit with the weapon.
There is one maneuver that I've gotten to consistently work when sparring with wooden sticks, which is to attack my opponents hand/forearm when they attack me. There seems to be a bit of an exposure which is an easy target if the opponent isn't being careful. We both use wooden sword and a kite shield.
I am generally pretty terrible at this stuff, and suffer more than my share of bruises, but that counterattack seems to work pretty well.
I suppose that a better attacker would make their attack less predictable, and perhaps my opponents haven't had the best form (they definitely tighten up quite a bit after suffering this attack once or twice), but making the attack has been relatively easy, since it doesn't have to go quite as far past their attack, or their shield. It does take careful timing.
It really may be a form problem, rather than a dependable response, since it is a lot harder to execute once it is expected.