Seems like bad business strategy to build on top of those if it means it's easy to steal away your userbase. Sounds fine for mid-size apps who can't justify rolling their own though.
If your only competitive advantage is user lock-in, then you already have a problem. Either you need to get your userbase to grow big extremely fast, or you've already lost.
And if you grow the user-base fast you've won, right? Lock-in and network effects matter enormously. Saying you can't lock-in the social graph neither guarantees a company won't lock-in elsewhere nor guarantees this is an appealing platform on which to develop.
This isn't a morality tale, I'm just pointing out what kind of decisions would be made around App.net and that the Vine/Instagram example doesn't really make sense.