1. A reddit-like circle jerk where the same stuff gets posted and the same conversations are had multiple times.
2. A reddit-like contingent of karma whores who repost stuff just to get votes.
3. A goldfish-like memory in HNers where they forget what happened just a short while ago.
The multiple posts about the same thing happen often when big stories break(Snowden's first leak, Steve Jobs death, Apple releases product iXYZ, etc.), but I'm noticing it now with some smaller stories, and it is frustrating.
My proposal is that the mods police these posts (I know they're watching, titles get changed all the time), and keep the front page fresh. When a big story breaks, maybe create a meta post- a "Snowden related links go here" post and when people outside of that official post they are either merged in or deleted. I realize it would require substantial changes to HN to add a meta post type and change the decay algorithm to account for a meta post.
Go ahead and downvote, but I figured I'd offer up an idea (that probably isn't original) instead of just complaining.
The fraction of HN users that see a post on average depends on how long a typical post stays on the front page and on how often a typical HN user checks HN. I don't know what those parameters are, but I think it's plausible that a typical HN user sees fewer than half of all front-page posts, in which case it wouldn't be surprising for there to be some re-posts.
If something changed about those statistics--for example, perhaps more posts per hour leads to a typical story staying on the front page for a shorter time--then that could account for an increase in the number of re-posts.
Also, I'm not sure that there is actually a trend towards more re-posts on HN. It seems like the kind of thing that would be easy to mis-estimate.
Sorry about the double post, but try to remember not everyone is glued to the HN front page or only doing things on recommendation from others :)
The best solution to prevent this from happening may be Stack Overflow style: suggest to the OP while posting the link that it has already been posted fairly recently and perhaps their comments would be better off in that thread.