[imported_Ryuuku]

If we did that then every other wep would do 25% less to them :p

What a lame argument.

Other wepon dont have damage based on wich creature its hiting so it dont afect them.

It same as say the +25 vanq bard did 100 on an undead creature before silver wepons added and now he do 75.
What is a lie, since you dont changed normal wepons to do less damag on undead, they hit the same as before.
What you changed is that now silver wepons do 25%+ on undead based on what it did if was a normal wepon (N: 100 , S:125), and 25%- on other creatures based on what it did if was a normal wepon (N:100 S:75).

So the normal wepon damg stay the same for undead or not.