Apple Client devices, such as the iPhone, and iPad, integrate much better when attached to a Mac running a MacOS... to many examples to list.
Applications written to the MacOS do not run on Windows (same argument in reverse that you made for windows only apps.)
The Mac user interface is not the same as Windows. For example, note top title bar of currently active application while displaying the application as a windowed application. Windows requires the application to be maximized to put the active menu bar at the top.
There are many differences. Each manufacture has a number of patents for many of these differences, some of which prohibit the msft/apple from poaching the ideas.
You didn't answer the question.
People use iTunes all the time on the PC. Since it is a browser based application, there is virtually zero difference in experience. You've got to do better than this.
Applications written for Mac?
You mean Photoshop, oops - runs FAR better under windows. Since Adobe hates Apple, I think they sabotage the Mac version, it actually shouldn't run as poorly as it does on equivalent hardware.
Fact, there IS no relevant software exclusive to Mac.
Personally, I find the Aero interface to be most functional for a keyboard and a mouse of the planet. But this is subjective.
For a touchscreen - nothing even comes close to Metro, which is why Apple is cloning it as we speak.