And no way MS hits fof 10k, it does not crit that high. Crit multipliers are somewhere about 1.3, and 10k would be 2.3 ish, from the top of my head. Way over stated.
Actually...
Yea yea horrible parse, I don't have any of the necro shadow line stuff
by debuffing the mob you are in effect lowering its level of abilities. Since the damage range given is assuming you are attacking a level 80 mob and you debuff its resists lower then that you will increase the damage the spell hits for.
Same way back when everyone was competing for who could have the biggest hit, they were dueling level 1 toons and casting IC or whatever...