DOTA isn't my cup of tea, but Valve's blog posts are often worth reading even if you don't give a sh*t about the particular game:
Our original plan was to spend the next year or so in beta, adding new features and slowly growing the number of heroes until we reached a level of parity with Dota 1, at which point we'd release Dota 2 to the world. But the feedback we're seeing everywhere is that people just want to play it, even though there's still a ton of heroes yet to be implemented. We've also seen that the folks who are already in the beta are chomping at the bit to show everyone else some of the fun games they've had. So we decided our original plan was dumb.
