Because someone posted it, and a bunch of people voted it up, and there's no downvote to express our displeasure with get-rich-quick junk or content-less Techcrunch stories or what-have-you.
There is. Flagging. And before you say it's "not for that", people are clearly using it as such. I've had perfectly legit posts (that I haven't "promoted" at all) slide way lower than their votes would indicate due to flaggers. So it seems a legitimate downvote system now.
Although I'm certain HN has been gamed in the past (search through the top results on searchyc for high traffic blogs and you'll notice a trend, and high upvotes with very few and completely worthless comments -- the effect of a content-less post), but in this case I'm not so sure.
I keep a hawkeye out whenever I see a post from a top blog on HN's frontpage, shit like this problogger, smashingweb, and mashable which are always either contentless diatribes or a bizarre summary of a link that's at the bottom of the post. There's a specific name for these types of posts but I forget exactly what. Anyways, this poster has a history if submitting from these major blogs anyways, so I think it's just a case of him/her being subscribed to their feeds.
The truly worrying part is seeing it with 100+ upvotes on the frontpage. That's not a good sign.