It's an alpha, while Rocket said that he isn't going to go out of alpha in ArmA 2. Say whatever you want, but the way DayZ grew makes the whole "alpha" thing unnecessary, especially considering that when DayZ finally gets out of alpha(probably 1-2 years), there won't be a fanbase like it has now.
Say what you want, but if Rocket develops this as if it is a closed alpha with a small amount of playtesters, he is doomed to fail and more and more people will start losing interest in it.