I disagree. As I understand it, Apple doesn't allow dynamically linked libraries on iOS. Loading an external SWF resembles a DLL somewhat at first glance, but not if you understand the specific implementation for iOS. In AIR on iOS, all ActionScript gets compiled to native code in the main executable. Even the ActionScript from external SWFs. AIR doesn't actually load the code from external SWFs at runtime. It's already in memory from the start. With that in mind, even if we "unload" a SWF, the code is still sitting around in memory. The graphic assets probably get unloaded, but never the code.
If I had to guess, it was probably difficult for Adobe to fully reset the state when unloading and reloading SWFs on iOS. On other platforms, they can start fresh more easily because the bytecode can be fully removed from memory. On iOS, that native code can't be unloaded, so it'll be in some arbitrary state when you try to load the SWF again. Adobe's only options are resetting its initial state (which is probably pretty complicated) or stopping us from reloading the SWF again later.