Well, the trend is so smooth that it would be very simple to apply a modifier to comments to counter it. Effectively, votes would slowly expire. In order to remain relevant, a comment would have to be constantly upvoted.
I actually think this would be an interesting experiment to try. Who's hacker friendly and has a well-used comment system that we know?
Yeah, seems good to me, in that it strikes a reasonable balance between keeping good stuff around long enough for you to see it, and keeping it around so long that you've read everything and get bored.
Thinking about this some more, though, I don't think I'd want to see the exact same algo on comments, though; comments don't have the same infinite-firehose problem, and you don't want to encourage spammy necrocommenting on old-but-still-popular threads just to get "new comment" karma.
Maybe something more like making vote fuzzing (which Reddit already does to some extent) inversely proportional to age, and actually sorting on the fuzzed value rather than the real one.
Basically, ant-algorithm. To stay relevant, you have constantly gather new votes. But it has one problem. Comments with higher votes already have momentum, hence they will be shown to new users most of the time, which gives it more chance to gather new votes, thus continuing the momentum.
I actually think this would be an interesting experiment to try. Who's hacker friendly and has a well-used comment system that we know?