The devs are people who work on the game - write the code, create the art, NPC quests, etc. Game Masters are the people who take care of problems between players, run events, etc. And they are around a lot, although they are from different time zones so you may not see them all together unless it's for a big event.
Events do happen very often, both small and large. But again remember that everyone is a volunteer, so our amount of free time fluctuates every now and then. One month there can be several events every week, and the next less.