If you read the presentation, it's more like,<p>>A: Facebook app has such different priorities than other developers, that Apple's development ecosystem has 'unreasonable' expectations and assumptions.<p>Facebook wants to be (and seems to like being) a "clowntown" (as the author puts it) where anyone and everyone can write up a duplicate library to anything and ship it. Any and all code will ship, it just can't make the app dip below 60fps. To meet those strange goals, they 'hacked' together their own GUIKit (at least three of them, actually), their own IDE, their own animation kit, their own debugger, etc. A general theme seemed to be that this was done in order to get everything off the main thread and onto background threads. By only depositing the very smallest amount of work onto the main thread from a gigantic soup of background threads you could keep the app snappy without needing to prune any code.<p>Seems to me to be a silly way to differentiate one's self.