Blogging gives the blogger a rewarding experience of being listened to - I wouldn't say that's a trigger, people enjoy being heard, so while they have listeners, they're gonna speak.

The reader on the other hand gets a new post, which could be about anything, and sometimes the post will be bad, other times good, really good. This will create a variable reward system, and keep the reader coming back.

Blogging can definitely be habit forming, especially micro blogging, or, tweeting. I just didn't think that's what he meant.