I think this is going away. I can play (some, and it's growing over time) Xbox and Xbox 360 games on the Xbox One, and if I bought them digitally or still have the original disc, I don't have to pay anything more.
Backward compatibility used to be way more normal. Then it was killed, now it is slowly coming back and we are supposed to be thankful for it. A more cynical mind could be tempted to think of this as a strategy.