As of Oct 10, 2011, the Facebook iOS SDK does again support the “apprequests” dialog for sending user-to-user requests from native iOS apps (see the screenshots in Facebook’s developer docs for an example).
One thing that’s missing compared to the apprequests dialog invoked via Javascript, though, is the possibility to enable the so-called frictionless requests (see the section about frictionless requests about halfway down the page), i.e. the ability for the user to allow the app to send user-to-user requests without the dialog popping up every time by checking a checkbox when the dialog pops up first.
Question: is there a way to enable frictionless requests for native iOS apps.
To answer my own question, frictionless requests now work (as of late Oct 2011). It seems Facebook has enabled the functionality.
The reason it worked all of sudden might also have to do with us switching our FB app ID from a sandbox app (for internal testing) to an app used in production. So perhaps frictionless requests are enabled by Facebook only for production apps or on an app-by-app basis.