Part of that though is because they _don't_ allow PWAs. Contrast that with Android, where it's now entirely possible to make a PWA so deeply integrated into the OS that the average user can't even tell it's not a native app: https://blog.chromium.org/2017/02/integrating-progressive-we...
Oh, but quite many will be able to tell after 5 seconds of using it. The rest will realize the moment the Internet connection drops temporarily.
Nope. A properly-written PWA will continue working just fine when the user goes offline, just like a native app would.