Personally, I don't think that introducing VP/WP will turn the game more realistic. In fact, it will make explicity anunrealistic feature of d20's hit points, which is the WP factor. Also, I think it is a poor design choice to have two stats that, in essence, represent the same thing. Hit points increase with levels is justified by the fact that the character becames a better fighter and so more able to avoid killing damage. However, this is exactly the same fact simulated by the defense stat and therefore my complaint.
If you really want to make it more realistic, consider using a fixed hit point value. Perhaps Con or Con+1/2Str will be adequate. As hit points are fixed and represent the actual ability of absorving damage, you could use the defense stat without redundancy.
Regarding armor absorving damage, I have no issue with current rules. I interpret that any roll which is a miss because of the armor bonus is a hit where the damage was absorved by the armor. Unlike the hit point increase/defense bonus, there is no inconsistency with the armor rules. It may be simplistic but it does makes sense.