Well, I certainly hope that news.yc users are a bit more than Ricardo-programmed economic optimization automata. :)
One solution to older users having a perpetual advantage would be to implement some sort of aging of karma, or at least of the karma value used to determine throttling. Such a thing would actually be a win in terms of SNR--it doesn't really matter how karmic someone was a year ago, if they have only made low-quality posts/comments in the past month, they should be treated (in the submission system) as a low-karma user.
An addendum, stimulated by dinner with dfranke: under certain assumptions about the growth rate of the community, karma ages without any algorithmic intervention: as the community grown, the number of moderators grows, and so the mean and maximum moderation per post increases. As a result, new post are effectively weighted relative to old posts.
The problems, of course, are that there is some fixed point, and also that news.yc may not fit the growth model that makes the above true for a community like Reddit--and that may be a good thing.
One solution to older users having a perpetual advantage would be to implement some sort of aging of karma, or at least of the karma value used to determine throttling. Such a thing would actually be a win in terms of SNR--it doesn't really matter how karmic someone was a year ago, if they have only made low-quality posts/comments in the past month, they should be treated (in the submission system) as a low-karma user.