third party app store

That's a very sensitive (and big business) topic.

Apple's main argument (which I share) is safety: they can control (pretty well, even though not perfectly) what goes on the AppStore to avoid malicious apps, or to avoid spam apps that would steal the value of original developer. Others would not necessarily have the means or intent to do the same.

On the other side, they claim they want more freedom to do whatever they want… Which brings back to the previous point.