Hmm. I'm guessing all that means is that they're giving the developers more access to the protocol stack. We'll see what that means in terms of application functionality, but that explanation really doesn't explain how it's any different than how watch behaves today.
WatchConnectivity
Now you can take advantage of robust device-to-device communication between the WatchKit extension on Apple Watch and the containing app on iPhone. WatchConnectivity enablesApple Watch to communicate directly with known wifi hotspots using the new Tetherless Wi-Fi feature in watchOS 2. This keeps your Apple Watch app up-to-date, even out of range of the iPhone. WatchConnectivity also saves battery life by allowing the WatchKit extension to transfer new information for the iPhone app to use when it’s next launched, allowing for seamless file transfers between the Apple Watch app and iPhone app.
That's been my experience. I can shut my phone off completely and as long as I have a known wifi network available Messages and Siri have always worked properly on the watch.People have reported leaving the phone at home and getting messages and such when on a known wifi network, so it seems like there's no change in what the watch will do. The change is that third-party devs will now be able to take advantage of that.