More like they recompiled springboard and some other core iPhone apps to run under OSX. This is why you can use real Foundation types in the simulator that don

More like they recompiled springboard and some other core iPhone apps to run under OSX. This is why you can use real Foundation types in the simulator that don't exist on the phone (NSCalendarDate), why you can use OpenGL extensions on the simulator that don't exist in hardware, and why certain UIKit transitions (i.e. Curl) don't work in the simulator. All the simulator is doing is running UIKit, Springboard, etc. compiled for OS X and running in an iPhone-shaped window.