If this were a wiki or answers site, where you want one easy-to-find location for a given piece of relevant content, I think you'd be correct.
On a link stream + discussion style site (which HN appears to be), though, you don't really have any idea who's participating at any given moment, or who's seen/absorbed material from previous discussions. I've been reading HN on/off for about 3 years, I can only recall having seen this once before, and seeing it again is an interesting reminder.
Apparently others have seen it a few times and are tired of it, but by and large, I'd think the scoring system could handle the general opinion of the community pretty sell: if enough readers still find it to be new/interesting information, it'll stay highly visible. If readers are tired of seeing it, presumably it'll sink to the bottom.
