Ahh, but you miss the point.
I think Apple's endgame is to have iOS apps run in a layer upon MacOSX. I think in the next 3 to 5 years we will see the loss of desktop Macs, starting eith the pro and ending with the iMac. All products will be SSD, driveless portable devices and nice displays. Think various iPad models and Air models.
I think Apple has realized the cash is in the device and services market. Macs do well but I suspect dollar for dollar the ROI on R&D is not nearly as good as mobile devices. On top of that Steve may have the opinion that the anchored desktop is a vestiage of the past and needs to die.
I think the next MAc OS will allow iOS apps to run native in a window.
You are correct that it is hard to combine two very different UI systems. But as Airs and possibly future monitor products gain bigger touch areas more and more will be offloaded to the magic pad, touch pad et al.
Personally I think this solves many problems but abandons a huge core of Apple users. I think many applications lend themselves to a touch interface and iOS feel just fine. These will evolve nicely. But genres like coding, desktop design, graphic design, and many others need other forms of input and ways to make workflow easy. I think if Apple evenually abandon desktop computing the hardcore apps that do not find a way to evolve will wither.
That said, I suspect Apple will include other inout methodoligies into the OS providing a workable yet new system for us.
Steve has an end game. He is pushing the evolution of computer to a new place. We may go kicking an screaming because it is different. Personally I thought it was doom when the floppy left. Never missed them or looked back. I thought the iPod was an overpriced useless device. I was sure wrong. I thought loosing the DVD drive was ushed a bit early, but then I realized I rarely use mine, so Steve is probably correct here too. iOS is evolving as are computing devices. With the cloud, ultra powerful portable devices the need for a bulky desktop system is soon fading for most users. Steve's end game vision is to take computing to the next evolution and allow a neqw evolution. After all the mouse based GUI is rather old and Hollywood has shown us many other creative options exist. Steve and Apple are just pushing the masses out of inertia into the new age.
Yeah, they'll just throw a mouse/keyboard input system into iOS, remove Springboard and port Finder over and you'll have iOS for Mac... err.. wait, that's what OS X already is.
iOS and OS X share the same kernel, the same display sub-system and a lot of frameworks. The difference is in the GUI itself and input sub-systems. And you know what ? There's no way to merge those.
So frankly, all these "iOS and OS X are merging!" posts are frankly completely ignorant of the current state of both OSes. There never was a gap to merge in the first place.