I ask because we would be foolish to think the developers of some less then typical quality apps have, or will, certainly exploit this for their own monetary gain.
Not sure yet. Path is actually the first (and will certainly be the last) social network I've ever joined - and it was precisely because it was supposed to be private and they had a pretty reasonable privacy policy. I remember something of this nature after the App Store was first released but had honestly thought it was a fixed issue.
On our lap/desktops we use prompting firewalls and on occasion will even watch suspicious apps or behaviors, if you will, where on iOS this is much harder.
I have an idle FreeBSD box and may start mitm'ing like OP did, but seriously pouring through the kind of output a home network produces doesn't sound like fun at all and I already know that going back to a dumb phone would probably be just as easy.
I would be curious for someone to do this with other apps. Even those that aren't social networks. I have a strong inkling that most of the top free apps are doing this without any of us knowing.