Well, to be fair, they released it way earlier for most gamers.
Most people are already playing for a few months now. But it's true, the whole "released, yet no campaign"-deal is rather weird.
I am not really a fan of the MP part personally, the ARMA community (read: those players in MP) take it way too serious for my taste. I am an ARMA noob and just for being bad, I've been flamed and even kicked. Not for teamkilling or griefing but just for being really bad
That turned me down from ARMA mp pretty quickly... So, I am waiting for the SP part cuz until then I probably won't even start it more than once in a while to play around a little...