Numerous other trend stories have been manually suppressed by HN's operators this year. The argument that a story is probably valid because HN's "anti-spam algos" didn't catch it probably doesn't hold water.
Well that just means their vote ring detection system needs improving. If there really is 100 people that have a vested interest in Bitcoin all collaborating on IRC or whatever and they are the majority of the ones pumping up the story then this seems trivial to catch.
Look at the distributions of the types of people that vote up the story, look at the differences in the average number of upvotes once it hits the front page, look at how many people flag it, but if you need to hard code things that legit users upvote you are basically imposing your view of what is good content over thousands of other people. This isn't a Viagra ad, this is a cryptography based, near-zero transaction fee, distributed, open source, online currency.
No wonder it always hits the front page, any of those five categories could hit the front page.
You just throw simple stats at the problem. You look at what a typical distribution of a normal submission looks like (30% of users < 60 days old, 20% of users < 100 karma, etc) and then you negatively weight submissions which breach the pattern by a certain sigma.
