Earlier quoted context omitted.
Have you seen the part where you can easily port iOS apps to macOS that was probably in the making for a few years? That's pretty huge for a developer conference. Changes to the app store to make discovery easier and feature more developer stories also have a huge impact on Mac/iOS developers and their revenue.
Is that an OS update? Do you really need iOS apps on the Mac? How about having decent apps in the actual native apps store?
They obviously can't put all the under-the-hood changes on the slides as there's probably a ton of stability fixes and hardening going on behind the scenes.
There are good iOS apps for a lot of things, if they can easily be adapted to run on the Mac as they demonstrated by porting the News app it can only be good for the ecosystem. The apps won't look like they are running in an iOS simulator and you use a mouse pointer to do touch actions. It'll be a normal native app that shares code with iOS.