Calling it a beta gives them some leeway in addressing issues in the build. Which, as mentioned, doesn't always work; I came across long reviews of Warhawk three days into the beta, from people warning potential future buyers from buying this "buggy mess of a game." To some degree, that's just the side effect of introducing something to console gamers that they are not accustomed to, but I can see why they'd want to avoid letting larger groups into early builds. I imagine the Resistance 2 beta will just be an advanced online demo, to fine tune it for launch.