Please forgive my ignorance, but where does it say it doesn't affect parrying? I've always played parries as not being affected by negative modifiers, but the OP has got me thinking that they are...
The rules state:
"Roll a D6. If the score is higher than the number your
opponent rolled to hit, the buckler or sword has
parried the strike. Note that it is therefore impossible
to parry a blow which scored a 6 on the roll to hit."
"Parry: Swords offer an excellent balance of defence and offence. A
model armed with a sword may parry blows. When his opponent rolls
to hit, the model armed with a sword may roll a D6. If the score is
greater than the highest to hit score of his opponent, the model has
parried the blow, and that attack is discarded. A model may not parry
attacks made with double or more its own Strength – they are simply
too powerful to be stopped."
and:
"Parry: A model equipped with a buckler may parry the first blow in each
round of hand-to-hand combat. When his opponent scores a hit, a model
with a buckler may roll 1D6. If the score is greater than the highest to hit
score of his opponent, the model has parried the blow, and that attack is
discarded. A model may not parry attacks made with double or more its
own Strength – they are simply too powerful to be stopped."
The basic Parry rule states that you must beat the "hitter's" roll, though the rule as it appears in the Sword and Buckler entries says "score" - I could understand the interpretations given above with the ambigiousness of the first entry, but when it refers to a "score", I think means it would be the roll -1 for the skill.
Is there something I'm missing?