One thing that really stands out in the Windows version of Safari is that it's exactly identical to the Mac version, almost down to the pixel level. That must have been quite a pain to achieve, and it would probably have been way easier to use the OS for many things. Does Apple really think PC users will go "gee, that Mac UI is really sweet, I think I now have an uncontrollable urge to buy a Mac"? Probably not.
So here's my hypothesis:
Safari for Windows is not intended to take over the Windows browser market, nor is it a showcase for the wonderful-mac-ui-that-if-only-we-knew-it-would-make-us-all-switch. It's an emulator.
Its one and only purpose is to make sure that devs who work on PC can build apps that will run on the iPhone and on the Mac. Especially the iPhone: when you have relatively little screen real estate, making your UI fit is no easy task, and the closer the browser on your dev machine is to the real thing, the better.
So here's my bet: when the final version of Safari ships, it will have an option to emulate the iPhone.