It's a wonderful place. It feels like HN, but with the Silicon Valley attitude dialed way way way down, and with a much narrower scope (politics, economics and entrepreneurship are all off-topic, for example).
I joined their IRC channel last week and it's been rather chill.
I do like the invite-only nature of the site though, keeps quality high...while making some folks tyrannical.
My intuition says it's to do with Status Signaling theory .