Turn on the "showdead" flag in your profile -- you'll see a lot of articles get [dead] the instant they are submitted. That's one countermeasure. If somebody starts at zero karma and submits nothing but links to one site everything they quickly have that happen to their posts.
Doubly recommend turning on show dead. You'll learn a good deal about implicit biases in the community as well. It can be fascinating and eye opening to see what gets buried, and a well placed vouch can go a long way toward bringing back to the forefront worthwhile discussions.
Yep, many good submissions, both links and questions, get suppressed by the automation and vouching for them is a great way to contribute to HN!
Survivorship bias. The bots that go through are so human-like you don't even register them as bots.