They share some similar characteristics, but thats not the same thing as saying they are mostly the same thing. Thats like saying oh I play basketball like lebron, we are mostly the same thing. Absolutely not, there are distinct differences that make them very different.
But not to seem like I am jumping on you, no hate here. Respect the comment for sure.
That's fine, respectful comments are always welcome, even when they respectfully disagree
But how big are the differences really?
The kernel is basically the same, the Unix-environment is the same (even though it won't be as complete on iOS as on a Mac), and the Objective-C stuff beneath the GUI layer is the same.
I would see the energy-saving enhancements to Mavericks as joint work on a joint kernel, no?
Of course the GUI layer is completely different, with UIKit throwing out a lot of legacy issues and showing more up-to-date approach to some things, and there are differences in the Objective-C runtime, AFAIK there's no garbage collection on iOS, you can only do RC/ARC, but that might well be a common feature in the runtime that's just disabled in iOS for energy saving reasons.
Then again it's not so easy to look into everything, for example one could question whether the device-wide search in iOS is based on the Spotlight technology, or whether something completely different is going on.