Contrary to popular belief we absolutely want to release games. When we say "we won't release a game until we think it's ready" that means we're going to make sure the systems are solid, and it's as bug free and stable as we can realistically expect of ourselves.
Ideas about design, our experience, player tastes and technology never stop moving forward, so when we refer to our game development process it doesn't mean we'll actually keep developing a game forever to have anything and everything we can ever imagine in it. We're going to at some point have to say "this is it" and get it into your hands.
The beta is privy to many in-process changes. If we made every beta patch perfect before releasing we'd be here for years. Part of the beta process is pushing out a build because you need X feature tested, and we don't care if Y and Z aren't done yet.