-I think the example you gave is a very rare case (I hope.) Unfortunately part of commenting right now is timing, which I do not have a problem with. If you post something informative two days into the conversation it will not have the same exposure, although depending on the conversation it will not appear far below the fold.
-I do see your point and I think it would be great if good comments that come late have more visibility. None or all of the following might help:
1) Delete comments and their replies once they reach a certain negative threshold (-5 for example.) Of course this gives downmodding a whole new meaning but maybe that is a good thing. This would make the comments section more readable and keep the conversation more civil and/or focused.
2) Highlight comments that were posted in the past 8 hours and have reached some karma threshold in yellow. This is a sort of "recent hot shots" feature. This way when an HN reader scans the page they can see what new comments are receiving upvotes more easily.
3) Give recent votes more weight then past votes. This means that a karma point awarded now means more than a karma point awarded an hour ago. Maybe the algorithm HN uses already does this- I am not sure.
I don't think pushing newer comments with fewer points up is a good idea because that changes the power up upvoting too drastically. Perhaps some anchor tags at the top of the comments section leading to the hottest new comments?
p.s. nice blog