You have to take into account the fact that iPhoto app has had many iterations. The binary plist stuff is very likely the native NSArchive "object archiving (serialization)" that is done by Obj-C libraries. They probably started using protobuf at some point later after iCloud. I suspect the unicode crap you are facing may even predate Cocoaization of the app (they probably used Carbon API).

So it would make it a set of historical decisions, but I am not convinced they are necessarily bad decisions given the constraints. Each layer is likely responsible for handing edge cases in the application that you and I are not privy to.