Except that on HN, if you are not getting more upvotes than the number of comments you are posting, you can't vote on the comments. That is what the "avg: " on your profile page is for, if it's not 2 or higher your votes don't count.
Is there somewhere to read up on all the rules of HN? I figured out a few things on my own (like that you have to have 200 rep to downvote), but once in a while I come across something I don't understand (like, it seems that you can't downvote immediate children of your comments?).
This kind of thing also tends to change. I think I got my downvoting privileges at 50 or so. Like words after a long night of drinking, voting has flowed a lot mre frequently of late. Pg usually modifies the caps to compensate, but they aren't usually announced. I noticed, for example, that /leaders is no longer in the top bar. I think that was a while ago, but just an example of how the site changes.
Here is pg's announcement: http://news.ycombinator.com/item?id=1173801
In the same discussion, in response to http://news.ycombinator.com/item?id=1174132, pg moved the leader link to the Lists page and had the Ask HN on top bar.