I don't think it's a big deal that Apple reserves some API functionality for their own apps — you can always re-create this from scratch, after all. They just aren't ready to fully support the popover controller API on iPhone. I'd rather that Apple be committed to every public API they publish (they aren't, but anything in that direction is a good thing).

What I don't like about this is how they chose to implement the restriction. Messy, hacky and inelegant.