This is, by far, the most important point. Google could make it very easy for you to use their apps offline, but they don't. The recent searches in Google Maps not being saved offline is especially annoying to me personally, and Google seems to think that it's impossible to store data if you don't send them to Google.
I can see them saying "we didn't want to confuse customers who thought syncing was broken when they didn't see their searches in other phones", but given how easy it is to tell the user "you have disabled sync", I don't think there's any excuse for Google to behave like this.