Earlier quoted context omitted.
Those sites are far smaller than Stackoverflow. Bespoke campaigns don't always pay more, and usually mean less total revenue for the site if that's all they run.
Tell that to John Gruber over at DaringFireball - He makes $6500 a week just from posting one ad in the RSS feed. If he can gross over $300K a year on a niche Apple blog without a sales team, can you imagine what a sales team could do at SO? He also sells three ad spots on his mostly weekly podcast for $6000 each. He’s a one man business grossing over 1 million a year without a sales team.
1) He has a sales person that sells ads on his podcast: http://neat.fm
2) Extrapolating from published rates is not very reliable. Nobody except John Gruber and his accountant knows how many sponsors really pay the sticker price.