Purely conjecture but I wouldn't be surprised if Facebook has an automatic curation system that will escalate content to human observers based on some kind of priority queue. Zuckerberg posts which are essentially PR moves? Priority: 1.

I wonder if he doesn't even realize it, thinking instead that Facebook and internet communities as a whole are entirely positive to him and his company (despite the fact that he inevitably spent time in the grunges of the internet in his earlier days).