If you watched D5 where Bill Gates and Steve Jobs were interviewed together it's mentioned that iTunes has about 1/2 a billion desktops installs and that iTunes could be used as the delivery mechanism for Apple on Windows and any other platforms for that matter.  Steve had a wicked grin he quickly suppressed and diverted the questions away from this idea.  Now that's what they are doing.

Apple isn't trying to take over Windows, they are trying to make it irrelevant, because the browser or whatever the link to the web and content and applications are, and that can be iTunes.  With Safari on Windows they are just making sure that they stay relevant and now can innovate on Windows and maybe tempt some Windows users to live inside Safari when doing things inside of iTunes.  Eventually more and more features would be added.