Okay so the Official Email from YouTube that explains the situation, at least how they want us to understand it, says:
"Here's why this is happening: You may have heard that we recently announced YouTube Red - a new membership that offers fans more choice in how they watch their favorite videos with features like ad-free, background and offline viewing for a monthly fee. In order to deliver a great experience for fans who choose to pay for this offering, we are updating our contracts with all of our content partners. The new terms make it possible for us to share subscription revenues with creators, providing an additional revenue stream for them beyond ad-supported YouTube revenue. The overwhelming majority of videos on YouTube are accounted for in our agreements, but there are some partners who have asked for more time to think about their options. While we work with these partners to update their terms, we unfortunately can't make their claimed videos available in the US."
From how I read it, it seems that in their implementation of YouTube Red, they haven't fully negotiated the rights with every copyright owner to remove adds (for the YouTube Red users) on videos with the copyright holder's content in them.
So how do they create an entirely add-free YouTube for the Red users while still launching YouTube Red on their timeline?
Block all the videos they currently can't apply the service to in the US for the time being.