Delta updates have been available for years now. When you go to the update pane in the App Store, the size of the app listed there is the full download version, not the update size. When you click update and if the original app size is over 100MB, you get that pop-up, but if the app update itself is under 100MB it will continue the download. If the app update is over 100MB, the download will pause until you are connected to WiFi.