* Attendees. I think the author did a good job of explaining what they get out of conferences. Travel! Diffuse connections that may or may not turn into more later, but are missed when not available. Plus some incidental learning.
* Sponsors. These folks put up some money to have a seat at the table. As a sponsor, you can support the community and get a good reputation, recruit (as author mentions), or have sales conversations. That's about it.
* Speakers. These provide content for the attendees. Either paid (devrel) or on their own initiative. Speakers want to share their ideas, increase their brand, and connect with others (speakers and attendees).
It's tough to put on a community conferences without all three of these actors being present.