Edit: Sorry, I think maybe you are asking why HN doesn't enforce article URL uniqueness - I can't answer that.
> maybe
Yes. The system here normally seems to check uniqueness.
It seems like submissions that don't get much traction after a day or so don't get counted as duplicates if resubmitted. There were 4 submissions of this article, and until this one turned back up today (second chance pool, this one was originally submitted 3 days ago) only one submission actually had any traction, and that was from yesterday evening.