Remember that Paul Graham was a key leader in the early days of spam fighting using Bayesian filtering etc.
http://paulgraham.com/better.html
Spammers aggressively try to game email. Likewise, promoters aggressively try to game HN.
How do promoters try to game HN?
Voting Rings
If you're not familiar with that term, a voting ring is basically a group of people (or robot accounts) that collude to upvote certain stories.
It shouldn't be surprising that Paul Graham would take a similar approach to Voting Rings as he did to Spam.
In one of your comments, you said: "I know it doesnt work because I click upvote and it doesnt assign any points while a friend sitting right next to me could do the same thing and assign points."
If you and another account always seem to upvote the same stories, yet no one else seems to upvote them at the same rate, then it starts to look like a voting ring.
Just like with spam, there will be false positives. I've heard of this happening to folks who have an audience that are also largely HN users. When they send out a new post, then many of that audience upvotes the post, but since it's often the same people, the voting-ring protections get triggered and the post will quickly drop off the front-page.
There are probably many signals that pg uses to detect voting rings. I'm sure they're not perfect, but I'm glad they're there. Otherwise HN would be overrun by aggressive promoters and HN would quickly lose its usefulness.
Advice to promoters: 1) create valuable content that helps users be awesome (no one cares how awesome your brand is), 2) submit it to HN, and 3) don't ask your audience to upvote it
Many promoters just can't help themselves and will do #3 anyways. Just be forewarned that you will likely trigger the voting-ring protections and will be shooting yourself in the foot.
For help with #1, see http://shelby.tv/video/vimeo/54469442/kathy-sierra-building-...