Can't downvote replies to my comments, is that new?

To the best of my knowledge one has never been able to downvote replies to one's own submissions or comments.

That's correct.

Ahh ok, thanks

I suspect the idea is that downvoting is not a productive means of rebuttal. Perhaps in part because the author of a comment is less likely to be objective in regard to contrary positions taken in child comments.

When I don't like a replying comment, I have to ignore it or use my words.

I think you explained the rationale for this mechanism perfectly.