I don't think Total Defense means cowering behind your shield. It means devoting all of your combat ability to defense, not attacking, but rather focusing on deflecting incoming attacks.
You've seen it in swashbuckling movies, where the "master" is toying with a lesser swordsman, making no attacks but easily deflecting everything the lesser throws at him (making witty comments as well).
I suppose the argument could be made that this is exactly what Combat Expertise is, but I'm still not sold on Total Defense being less defense-effective than attacking (but then again, the maxim is "The best defense is a good offense", so maybe I'm just flat out wrong).