Were the reddit devs aware that they were making those posts? I'm guessing yes, but I'm guessing that easily 50% of those "posters" over at O'Reilly Overflow have no idea what they've been up to.
Were the reddit devs selling their books by posting? (Yes, I understand that Reddit sells stuff, but the posts are not directly linked to selling what they're posting about. That's what makes the O'Reilly site astroturfing.)
When reddit launched, nearly all the posts were by reddit devs or YC insiders. Give it time to see if the model takes off among external users.