That's because some posts get flagged by folks who either think it doesn't belong on HN, or that it spam/offtopic/flame and the posts move downwards.
However, sometimes people seem to flag posts because they don't want them see by HN readers. I've seen this happen to a lot of links to stories that aren't charitable to Google/Apple or are friendly to Microsoft even if they're legitimate news stories or even just announcements.
Also wanted to mention that lately I've seen even some Apple news and announcements get flagged a lot. I speculate Google/Android fans/employees/shareholders are going a bit overboard. :)
However, sometimes people seem to flag posts because they don't want them see by HN readers. I've seen this happen to a lot of links to stories that aren't charitable to Google/Apple or are friendly to Microsoft even if they're legitimate news stories or even just announcements.
Edit: HN Rankings shows a huge plunge from #2 to #50 in five minutes http://hnrankings.info/5010891/
Also wanted to mention that lately I've seen even some Apple news and announcements get flagged a lot. I speculate Google/Android fans/employees/shareholders are going a bit overboard. :)