Thanks for your thoughtful and detailed response. I genuinely agree with effectively everything you're saying.

As an aside, there is another way of looking at your same examples: effectively all of the services you listed continue to exist, sometimes even after 20 years, albeit repackaged or renamed with only in the worst case a hiccup for users to migrate. In the case of the chat functionality from G+, it simply evolved to what it is today. Perhaps I was too harsh and strung up on the remark about discontinued services.