I agree that OS X Updates often do require one reboot, after the software update process is complete. This is still much better than Windows: Incremental Update, reboot, incremental update, reboot, etc....
As far as UAC goes, this is more of an example of a new, MS proprietary idea badly implemented that was used instead of embracing alternative security models that have existed for decades under UNIX.
I'm not saying that other OS's don't have proprietary components, but if I write a program in Visual Studio with C++ and use Direct X or MFC, how do I port such a program to linux? I really can't. In the end, I would have to re-write most of the program.
Compare this to proprietary UNIX-based OS's where ports are much easier to accomplish between systems.
The purpose of technical standards is to integrate technology across vendors, which, does not really exist under the Microsoft philosophy to control their majority market share. So Microsoft's claims of compatibility are only true if you are using another Microsoft system.