Yes, iOS and OS X are basically a single OS. Only they support different hardware platforms, run completely different apps, provide completely different SDKs, have completely different UI guidelines, and serve completely different use cases.
Other than that, who could tell the difference?
The reality is that the AppKit (OS X) and UIKit (iOS) SDKs are actually diverging, not coming together. There isn't so much as a hint of traditional keyboard+mouse UI support in the UIKit SDK, which means that iOS apps are not coming to mouse-driven desktop anytime soon. And while many new AppKit features are inspired by iOS (e.g., view-based table views), the AppKit engineers have made no effort to keep those features source code compatible with their iOS counterparts.
Apple has made it clear. These are two different SDKs on two divergent paths.
Not to mention even the most basic Foundation data structure classes are different. iOS's Foundation comes with less data structures than OS X's and has different performance characteristics tailored to mobile hardware.
Other than that, who could tell the difference?
The reality is that the AppKit (OS X) and UIKit (iOS) SDKs are actually diverging, not coming together. There isn't so much as a hint of traditional keyboard+mouse UI support in the UIKit SDK, which means that iOS apps are not coming to mouse-driven desktop anytime soon. And while many new AppKit features are inspired by iOS (e.g., view-based table views), the AppKit engineers have made no effort to keep those features source code compatible with their iOS counterparts.
Apple has made it clear. These are two different SDKs on two divergent paths.