You are probably basing your statement on traditional Asian marital arts training (I am assuming you to be a student/practitioner to give you respect and the benefit of a doubt). So I can see why you would believe that is how it is "in real life".
And it is true, that is how it works about 50% to 90% of combat time when you are blocking with the same weapon you are attacking with.
However for about 90% of the time one is in combat (using a shield) that is not how it is done in real life. Otherwise I guess I have been doing it wrong for over 30 years and still manage to gain our world wide organization's (SCA) top 1% ranking. I have been ranked as King twice and now hold the rank of Duke as well as Knight. (my credentials: http://wiki.caid-commons.org/index.php/Patrick_Levi_Darkwrath )
I am very sad about this and I do not know why. I should be happy that one of the best game companies on the planet is falling back once again, like every other game dev, on the Asian (game logic) template that a 10 pound one handed western European shield == 2h three pound katana blade. I should tell myself this means I still have huge opportunities in the game industry to make big changes once I am proficient enough in animation or other game making skills.
The shield if used properly will move only about %10 of the distance and speed that the attacking weapon will. In layman's terms, shield work is (in general) maintaining the shield in position (angle and location) relative to your opponent and you that denies an open path to the most likely targets. When your opponent goes for the less likely targets you as a shield man first take a step to close the path, then if that is not enough you turn, if that is not enough THEN you move your arm. Tricking your opponent (or getting them too tired or many other techniques) to move the shield out of its defense position is how you kill them.
This is an extremely simplistic explanation as there is an entire science to what I coined as "Combat Geometry". But with your background in marital arts I hope you will understand what I am saying.
see here for more info about combat with Shields: http://www.spookyfx.com/book/tromp.html
I am more depressed about this then I should be, but I think it is because from what I have read about this I fear I will not be able to mod this out of the game.
I need to remember that this is all speculations I guess, wait to see how the game really is, then go from there to see if I can tweak it to be more fun and realistic. Todd and his team seem to have the vision, thick skin and bravery other companies do not have to allow their game to be as "mod-able" as is practical.
This is one of the things I'm excited about with the new combat. What idiot is going to swing and intentionally hit your shield anyway as you sit there and hold it up? You wait for them to start their attack, then raise your shield to deflect it. That's how it works in real life.