Safari for Windows was released more than a year before the first Google Chrome beta. Before that, Webkit wasn't available on Windows at all and it was impossible to test websites on Webkit without a Mac. Google Chrome is now an excellent and widespread browser on Windows so there's no point maintaining Safari for Windows anymore.
I have encountered more than one bug that exists in either Chrome or Safari, but not both. If you only test using Chrome on Windows, you still won't really know how it will behave in Safari.
