The convention idea roundup is here.
A once-yearly convention is not really a yearly thing – as anyone who has run one knows from painful experience. There is planning, there is community moderation, there's getting the next hotel. For some, they can forget the convention for most of the year, but for many others, they cannot.
Of course, there are many good things about conventions that go on year round – the message boards, the chats, the planning get-togethers, and so on. These things keep the attendees and the staff primed, give them a chance to socialize, and build the "con community."