It looks like Apple is discontinuing support for Safari on Windows. With the release of Mountain Lion last week, Safari was updated to version 6. However, there is no Windows version 6 of Safari. When you go to the Apple website for Safari there's no download option if you're using Windows. However, if you Google for Safari 5.1.7 you will see that there is a link to a support site that has the download.
Here are a couple stories detailing the change.
SitePoint: Dropping Windows Safari is a Mistake
MacWorld: Safari 6 Not for Windows
I have to agree with the SitePoint Writer, getting rid of Safari on Windows seems like a bad idea. Although it is not that popular it is very useful as a development tool. Maybe Apple should consider open sourcing the Windows version? It is important for there to be another WebKit browser on Windows other than Chrome.