Why post a link to compete.com when pg has just discredited as a source for meaningful information?
A similar comparison on Google reflects little change for the others:
http://trends.google.com/websites?q=news.ycombinator.com%2Ct...
That said, it relies on GoogleToolbar/Chrome, but we could argue that it's distribution amongst visitors of those sites is going to be pretty similar.
Edit: Updated to include mashable.com