Agreed. These purchases seem to work the best when they're used for defensive purposes and to round out a product offering that already has a substantial userbase.

Whatever gadgets they might hang off the app, they're fundamentally a way for people to talk to each other. If you don't have the people, why would you need a slick implementation? As you mentioned, the app would go out of vogue and users would move on.

Amazon making a bid here sounds like a play for a decent social seed, likely steming from users of its core properties (shopping and dev). Of all the mega-corps, Amazon is one of the few that has all the pieces and user-engagement, but no social component.

Which is ironic, because their properties would play a lot better with one than, say, Google or MS. And starting with something like Slack (bottom up vs top down) is an interesting move.