Hi OP,
I think a lot of views come from people that see the title, "Stats on Warrior" and hope to find the answer, then see the question they have.
Kaeko of Figaro and several others have done some testing here:
http://kanican.livejournal.com/55915.html
One of the things I took away is that Vitality does reduce the damage. The amount of damage reduction is not reflected in defense.
Defense also reduces the damage received from physical attacks.
There are some other factors involved that determine how effective your Vitality and Defense will be.
Similar to how a Weapon has a Damage stat that has a large impact of how much damage we deal. But using a weapon with a low Damage value or a high Damage value does not update the Attack Power value, but we still do more physical damage.
Anyhew, the link has some really interesting testing in there.