I personally don't like people downvoting critical reviews by default and I think it should be discouraged. Like it or not though, people are naturally going to give more scrutiny to negative reviews than positive ones. I certainly wouldn't consider posting something as dumb as my current QBJ3 review (at least the one there right now, maybe I'll do something more substantial later) if my over-all evaluation, and therefore star rating, were not so positive. Even so, clearly some people didn't appreciate it and mine sits one point below yours at present.
I thought some of the negative points of your review were reasonable, and even agree with a subset of them, but I found many confusing and/or petty, so I wouldn't discount every downvote as instinctive either. Rounding the rating down probably felt overly harsh to some people too. But again, they're more likely to seek out things "wrong" with a review if they already disagree with the rating before reading it.
It doesn't affect anything but the number next to the review itself, so I don't think there's any reason to be concerned. If that does still bother you, my suggestion would be to not dish it out if you can't take it. You can also post an anonymous review, or a rating with no review, if it makes you feel better.