Facebook’s iPhone app seems to integrate with the Facebook Platform using the same rules that other applications must follow. After you sign in to the iPhone app for the first time, a corresponding Facebook app, Facebook for iPhone, is automatically granted access to your profile.
There is nothing unusual about this; Facebook is merely playing by their own rules. But there is an interesting side effect.
Facebook is a social platform, so all application pages allow you to list other friends using that app. Facebook for iPhone, the Facebook counterpart for the iPhone app, is no different.
These are all your Facebook friends who use (or once used)…
It is worth noting that the Facebook for iPhone app remains in your profile until you explicitly remove it, so results may be misleading. (After all, how would Facebook know that your iPhone fell into the toilet, when you may simply not have run their app for a long time?)
If any of this bothers you, breathe deeply… then get off the internet.
And my lawn.