To me, it's weird that this thread existed in the first place. There are lots of videos (including Apple's iPad Pro video) where palm rejection is shown. So it's obviously possible. That's where the thread could be closed already. Whether or not it is applied in all apps is a pointless question then, as clearly not every app neds to have or should have palm rejection.
Given what was shown at the presentation, there was reason to ask the question. Yes, there is support for palm rejection in the iPad Pro/iOS 9. But the follow up question becomes, "is it universal to the entire system or must app developers code support for palm rejection?"
It looks like there are APIs available to app developers to support palm rejection when using the Apple Pencil, but the apps must be written to use them. THAT would explain why so many of the Apple Pencil demonstration videos show the hand floating uncomfortably over the screen using some apps, and hand resting on the screen in others.
During the presentation, the guy at the iPad Pro demo'ing Office for iPad with the Pencil was very careful and deliberate to not have his hand come in contact with the screen while using the Pencil. That led me to believe that Office didn't yet support palm rejection.
I suspect that over the next month there will be a lot of scrambling of developers updating their apps to utilize these new APIs.
In the end, it is a step better than what was available before (homegrown logic written to support palm rejection in a particular app). But it isn't as good as a system level support that makes palm rejection transparent to the app.