Okay, lots of confusion happening in this thread, so let's try to clear up some of the muddy waters.
- Smart Delivery is not the same as "X Enhanced Patch" or enhanced backwards compatibility. Currently with the Xbox One X, you have some games that have been enhanced for the Xbox One X that is downloaded to your console. Also, some BC games are enhanced for Xbox One X, like higher resolution, HDR support, better frame rate, and more. Smart Delivery does this, but goes beyond it. If there is a XsX sku for a product then that is what is being delivered to you, not just an enhancement patch. In previous generations, you would have to pay for the game twice (Titan Fall and Assassin's Creed IV: Black Flag both fell victim to this at this generation's launch). Now you don't for the supported games.
- Smart Delivery handles the back end portion for developers where it comes to handling the downloads/licenses. The developers still have to make the XsX sku along with the Xbone sku, with both having their differences for the two different consoles. However, MS does the handling of automatically allowing the customer to download the XsX sku to their console after the Xbone sku has been purchased (either through disc or digital). Before, third-party developers would have to include a download key in their packaging for the update, or some other system (like an account on their website that would link to your Xbox account, gifting you the game). With Smart Delivery, that portion is removed for the developers. If the game is included in the system, MS will manage the license for the customer to automatically download the XsX version of the game.
I know many argue that this is the same as Sony's Cross Buy system, but it really isn't. What Sony did with PS3 games and with the Vita was great, but it was not for all of their first-party games. Not all first-party games could be played on Vita vs the PS3. Looking at the list of PS3 to PS4 cross buy games, they are mostly smaller PSN games. I do not see any big first-party games. When you look at a game like Gran Turismo 6 that was released after the PS4, but was only available for PS3, you wonder why Sony did not make a PS4 version and why it would not have been cross buy. Where Microsoft is going all in on this, Sony was reserved.
Going from the WiiU to the Switch, Nintendo released a lot of games on both consoles, with improvements to the Switch version. Wouldn't it have been nice if those of us who already purchased those games on the WiiU (the few and the proud) could transferred those games over to the Switch, without having to buy them again? Smart Delivery gives us that.