You can get a look at release notes if you open the Mac App Store first before restarting.
But for example, if you are testing Mavericks Server you need a download of a matching Server App after your machine has updated its OS, so the lack of the Mac Developer Portal is still throwing a monkey wrench into things. If you are testing Server I'd recommend waiting for the website.
I assume they could push over the air updates for iOS as well. But if an iOS install fails, your fallback would be a device restore in iTunes. And I'm afraid without the downloaded iOS package you would be really stuck. So its probably for the best that nothing has yet been released.