I agree with this policy. It sounds totally benign and ordinary.
I haven't been particularly encouraged to try responding to comments, either.
If you mean comment karma, consider that in the case where people appreciate your responses, but strongly disagree with their content, they will downvote you instinctively, as soon as they would furrow their brows: it's an immediately available, low effort way to scratch the itch of dissenting feelings. Since downvotes seem to give you cold-stabbies, but don't make you reevaluate your positions, instinct-downvoting is doubly ineffective, but still the default. We've now learned that saying "This isn't a poll. You have to correct me or I won't stop being wrong", isn't enough to break that habit.
Indeed, and we (the LW community) have to learn to tell the difference between deliberate trolls and misguided rationalists for our moderation to be effective. In the same way that replying to a troll is a mistake in that it feeds their attention craving, not replying to a wrong non-troll can be a mistake in that they don't notice their error. Maybe a lower downvote limit (4xkarma) would help break aforementioned habit.
http://wiki.lesswrong.com/wiki/Deletion_policy
This is my attempt to codify the informal rules I've been working by.
I'll leave this post up for a bit, but strongly suspect that it will have to be deleted not too long thereafter. I haven't been particularly encouraged to try responding to comments, either. Nonetheless, if there's something I missed, let me know.