Dota2 hasn't even been released yet. People are still playing a test version. It's still possible (though unlikely) for a simultaneous Windows/Mac/Linux release!
Meh, that's a weird nomenclature game. It's beta like Google Maps was for the first six years of its life. Valve is selling and running international tournaments on this "open beta." Like, it may say "beta," but it is definitely released. You can go on Steam and buy it right now. They even have a separate test client in addition to the nominally "beta" normal client.